Physics Graduate EXPLAINS Physics Paper 2 2023 GCSE Science

hey guys welcome back to another video this time we're doing another gcsc physics paper this is combined science paper 2 June 20123 so I did the paper one a while back a lot of people wanted uh the paper two for it so we're doing the paper two um before we get into the video though if you've ever found any of these videos useful please do consider subscribing and also consider either emailing me or visiting the website if you're interested in some kind of tuition right before the exams for GSC and for a level but let's jump straight into this with question number one so here we have a question on electromagnetic waves the sun emits a continuous spectrum of electromagnetic waves figure one names some of the groups of waves in the electromagnetic spectrum and a few of them are missing uh name groups a b and c in figure one so there are two strategies to this uh the first one is of course writing out all of the different electromagnetic waves and seeing which ones are missing so a few of them that are missing are radio we also have microwaves are missing from here and x-rays as well those are the three that are missing from this electromagnetic spectrum now you need to think about which ones go where right so we have all three but bear in mind that you have to get two correct well sorry three correct to get two marks and to get one Mark you need to get two correct so you don't have much room in the way of guessing so here's how i' think of it as you go to the right the electromagnetic spectrum gets more dangerous so it's less likely that you actually want it to be you know anywhere near you so infrared for example it keeps things warm so hot objects release this visible light well that helps you see so that's fine now UV is where it gets interesting UV radiation is what gives you sunburn so it can give you skin cancer so you know as long as you wear some sunscreen you're totally fine then we have a blank then we have gamma rays which are extremely bad for you they'll give you some kind of cancer or they give you super powers so what goes in between them well if you think about from the ones we have left over we have radio microwaves and x-rays now radio waves they are everywhere all of the time CU they allow us to pick up well radio signals for TV and also for radio shockingly um microwaves most people have them in their houses it's completely fine so C must be x-rays because that's the only one where there's some kind of danger involved right so if you've ever gone to get an x-ray and the doctor goes H and runs out of the room and hides behind a massive screen for example it's because it's dangerous now A and B well if you think about about microwaves and radios waves which ones are more dangerous well microwaves if you notice when you have a microwave they are contained inside the microwave and it isn't really advisable that you put a body part in the microwave and turn it on um and radio waves can just be literally anywhere they are super low energy so they don't really interfere with you so a is actually a radio wave and B is actually the microwave in this case so again from left to right so from longest wavelength to shortest wavelength or lowest energy to highest energy however you want to look at it or lowest frequency to highest frequency they get more and more dangerous is the way I like to think about it but it's up to you now it says give one similarity and one difference between the properties of UV waves and gamma rays well the similarities there's quite a few the first one is that they both are transverse waves that can be a really good one they both transfer energy because all waves transfer energy and lastly the best one is that they have the same speed so travel at the same speed in a vacuum same speed which is the speed of light again in a vacuum yeah in terms of similarities you're just thinking because they're both electromagnetic radiation well what kind of waves are electromagnetic waves right well they're transverse waves they transfer energy they travel at the same speed Etc now the difference well the main difference is is wavelength or frequency those are the only two that I would B bother with but I will tell you a few others so I've use Lambda for wavelength and F for frequency again you should write out the full thing like wavelength or frequency um you can also say about gamma radiation being more ionizing more penetrating something along those lines or even more have sorry they have more energy anything along those lines will be completely fine but for me I like to stick with the most obvious the easiest thing I'm super lazy I would just stick with wavelength Andor frequency so for part three we have white lights being split through a prism into its constituent lights and part three says lights changes Direction when it enters the glass prism what is the name given to the process that is just refraction um there's no real fancy fanciness there if it's passing through it then it can only really be refraction um and also it's changing direction right so refraction again let's have a look at part four and part five using the equation sheet nice write down the equation that links frequency wavelength and wave speed again we've seen this a lot where part one the first part will be write the equation the next part will be use it to do some calculations it's super super common it comes up all the time especially in physics and the equation there looking for is V equals F Lambda and again this is just looking at the equation sheet it's all on there for this the wave in the middle of the spectrum has a wavelength of 5 * 10- 7 the wave speed of light is 3 * 10 8 which is what V is calculate the frequency well if V is equal to F Lambda then if we use a quick rear ranging using our math skills then we want to work out frequency so we want to make frequency the subject of the formula what's stopping from being by itself the Lambda so we're going to divide both sides by Lambda by wavelength and we get V Lambda equal F and then all we need to do is sub it onto our calculator in order to work out the value so wave speed on top so 3 * 10 ^ of 8 over the wavelength 5 * 10- 7 we're going to get an absolutely enormous number because frequency tends to be quite massive HS for three marks I think that is absolutely Ely amazing and that's question one done nice and short nice and easy question two is about the acceleration of a trolley being affected by the force acting on said trolley and they give us some of the equipment used which is a trolley and a Runway okay describe a method the student can use you should include any extra equipment needed so there's a few different things so it says here if we read the question investigates how the acceleration of the trolley is affected by the force acting on it so what we're going to try and do is vary the force and measure the acceleration that's the goal here so we need to think of a way that we can vary the force acting on the trolley and honestly there are loads of different ways that you can do this the most simple way is by changing the height of this Runway because as we make the height of the runway higher then the Troy is going to you know it's going to accelerate faster right right because more of its weight is acting down the Run way another way you could do it is you could do and please forgive me for my drawing here you could attach a string to the trolley over the edge and attach masses to the um kind of end of the string and then when you let go the trolley will be dragged Along by the weight now this is quite dangerous because of course the weight's going to just fall and hit the floor the trolley is going to go flying off the edge of the table Etc it's not going to be it's not going to be the nicest thing in the world um so I would say using wooden blocks makes the most sense um you know to vary the height of the runway but yeah that that's what I would say so here is my method I'm going to vary the height vary the height of the runway using wooden blocks you could say of known height but that's kind of implied and here are the measurements that we're going to to take we are going to essentially find the height of the block so we're going to measure the height of the runway and we're also going to measure the time taken to travel a certain distance so what we could do is we could put a nice little marker on the edge over here and work and just basically use a stopwatch to measure the time it takes for it to go along here that giv gives us the velocity and which also gives us the time uh sorry the acceleration as well using a stopwatch um velocity equals distance over time and acceleration equals velocity over time as well so that allows us to work out the acceleration that because don't forget the acceleration is the actual independ variable is what we're measuring we're altering the force and altering the force by changing the height of the trolley um yeah that would probably be the best way to do it of course another way you can do it is using the the weights off of the edge of the table which again is totally fine you could do that now I would say this is kind of the best way to do it again just in terms of safety just you don't want to have things flying everywhere when you're doing an experiment once you found the acceleration and of course you have the height of blocks you can you know use that to work out the the force now the next thing is this is obviously only four marks because we've only made four points the next things you should talk about whenever you're doing an experiment is you need to talk about ways that you can make it more accurate so we can make the experiment more accurate by using a light gate to determine speed or time and you can also use a computer to calculate the acceleration I now have the spell calculate there and lastly you can repeat with different number of blocks that is also completely and totally fine but that's probably the best way to do the experiment is the safest way rather than you know hanging weights off of everywhere making it fly around table one shows one set of the results for a similar investigation so 1.2 Newtons as a resultant force and the acceleration is 1.6 m/s squ which of Newton's Laws predicts that the acceleration of the trolley is proportional to the resultant Force so in other words they're looking for f equals ma right because F and a are directly proportional always proportional in this case now is that the first second or third law this is just a memory game the first law is an object in motion will continue in the same motion unless acted on by a resultant Force so that means the acceleration uh actually not say acceleration basically there'll be no acceleration unless there is an outside force the second law is fals ma so that's the one we're looking for and the third La is every action has an equal and opposite reaction yeah honestly that's mainly just memory there's no real way that you could work that out per se but again if you could eliminate the third law then you have a 50/50 chance you know maybe that helps a little bit and it says determine the acceleration of the trolley when the resultant force is 3.6 Newtons now um let's do that since we have fals ma or in other words the force and the acceleration are directly proportional if I times the force by well actually no let's write it this way 1.2 Newtons equal 1.6 m/s squ this is like direct proportion in gcsc maths we've gone up to a 3.6 Newton force and now the question is what do I times 1.2 by to get 3.6 the best way to work this out is to Simply divide the two numbers so 3.6 / 1.2 gives me 3 in other words 3 * 1.2 gives me 3.6 so if I've times the left side by 3 what do I do to the right side if it's directly proportional again remember your GCC maths you also times it by three so we're going to do 1.6 * 3 which gives you 4.8 m/s squared which is the correct answer and once again we have a calculation so write down the equation and then perform a calculation the A M and F is just FAL ma a and once again they give us the resultant Force they give us the acceleration we want the mass so so we want to rearrange for M we want to make M the subject m is being Times by a so we do the opposite we divide both sides by a and we get force over acceleration equals mass so we get 0.42 over 1.2 so this is an absolutely tiny Mass but that's fine that's just the way it is in for2 / 1.2 gives me 0.35 kilo for three marks man such a lovely question nice and easy I hope okay so in this question we're going to have to um you're going to have to give me the benefit of the doubt here for a second but a teach uses a ripple tank to demonstrate water waves the teach use the lamp to project a shadow of the water onto a screen below so you put a lamp above then you have the Ripples and you have bright and dark spots underneath super useful super nice whatever we've probably done it before and it says 1 mm on figure 4 represents 5 M on the screen cool determine an accurate value for the wavelength now here's what you need to do you need to think about why there are dark and bright spots the reason is this if I exaggerate this for a second this is what the water wave looks like right when you cause ripples when I shine a lamp above it there is certain parts where the light only has to go through a little bit of water to get to the screen and there are other parts where the light has to go through a lot more water to get to the screen where there's a lot more water there will be less light that makes it all the way through which means it'll become dark where there's less water that it has to go through it will be light because there's less water for the light to go through so in other words these dark spots are spots where we have a peak in the water wave and the light spots are The Valleys or the troughs or whatever your teacher calls them the low points of the water wave so again the dark spots represent Peaks the light spots represent troughs or valleys whatever your teacher uses so if we want to work out the wavelength here all we need to do is think about what the definition of a wavelength is it is the distance between two adjacent Peaks or two adjacent troughs now here the dis the kind of white spaces are bigger than the dark spaces so it makes more sense to do it from Peak to Peak so you would measure this distance here and times it by five to get the answer now unfortunately I had to do this in real life and I've also used the mark scheme to help me out here as well the length that you get is 14 millimet now what you might want to do and I use the word might very effectively is to measure the distance for the entire thing how many wavelengths is that well it's one wavelength 2 3 4 5 6 7 8 so measure the whole wavelength which happens to be 113 mm because it's easier to read on your ruler and then divide it by eight to get one wavelength now why did I Times by five it's because 1 mm on figure 4 is 5 mm on the screen so you've had to times it by five cuz it's the wavelength of the waves on the screen now either way you do this it doesn't really make a difference if we do 14 * 5 you get 70 mm now you get a range the range is from 68 to 72 since this is millimeters you can only the the range is only4 cm it's very very small that's why measuring the whole thing and dividing is actually a smarter move because it's way easier to read a big number than it is a small number but that is kind of how you would do it hope that makes sense and I hope again the dark and the bright spots make sense because they can't ask you questions about that just because they haven't done so far doesn't mean they won't in the future the teacher adjusted the frequency of the Waves produced in the Ripple tank the teacher measured the wavelengths five times here are the results we have all these wavelengths and we have one that's blank and we have the mean calculate the value of x now this is actually very similar to a gcsc maths question now the mean is the sum of all values over the total number in this case it' be over five right because it' be you add up all of these wavelengths together 96 plus 99 plus 97 plus X + 97 / 5 = 97 so what we could do is if you work out what the sum of all of these numbers is we can just subtract all of the other numbers to get X so I'm going to take the mean and I'm going to multiply it by five which gives you an answer of I don't know let's quickly use a calculator um 97 * 5 gives me 485 so that's the total of all of these values added up that's 96 + 99 + 97 + x + 97 = 485 so if I subtract all of these numbers I should get just what x is so I'm going to minus if you want you can put it in Brackets you could be fancy with it you could do whatever you want but the idea here is I'm just going to subtract every single number in the table so I'm going to do 485 do 4 85 - 96 - 99 - 97 - 97 and I get 96 so X must be 96 very similar to those gcsc matter questions we have to work out like you know the mean score of the class is this the mean score of the girls is this what was the mean score of the boys or something weird like that the teacher states that the results are very precise which of the following supports the statement made by the teacher TI one box the mean value is very close to the True Value the spread of the values about the mean is small the values are all given to the nearest millimeter the wavelength measurement was taken five times so the difference between precise and accurate or precision and accuracy has been the bane of a lot of science teachers um for a very very long time because put it this way accurate means that you're correct so the answer is the actual right answer i' have no idea if this is the right answer there's no way to tell so it's not the first one because that is accuracy if you get an answer close to the real value then you're accurate so a good example of this is let's say you're weighing something that has a mass of 20 kilos and you find a weird way to me measure the mass and you end up getting 20.01 kilos that's accurate because it's very close to the real value now let's go to the next one the wavelength was measured five times this means that your measurement is reliable it means you can trust it if I do something five times and I get the same answer I can trust it it might not be right though and it might not be precise but I can trust it CU I've done it five times now the nearest millimeter honestly that's so and so that is kind of like Precision it's actually the spread of values about the mean is very small so Precision refers to how how many decimal places how many significant figures have you given your answer to in this case because all of our numbers are very close together we must have been very precise because there's very little difference there very little spread in the actual values about the mean I hope that makes a bit more sense describe the difference between longitudinal and transverse waves wonderful well the main difference is how they propagate through space or through a material through a medium whatever you want to call it longitudinal waves oscillate so vibrate parallel in the direction of um to the dire direction of motion so what do I mean by that they kind of move like caterpillars do right they contract and move along so the wave is moving this way and they're Contracting that way as well okay so if you imagine it it's like you get a spring and you push it going to the right okay now a transverse wave oscillate perpendicular to the direction of motion so I can draw the transverse wave one quite nicely is if you were to shake a rope up and down or a spring or a slinky whatever you want to do you might notice that the peak right so when you shake it it's like this right and the rest of it's flat as time goes on the peak moves to the right so this goes up and down but the actual whole wave itself is moving to the right it's moving perpendicular so it basically looks like this as it goes along whereas a transverse wave sorry a longitudinal wave compresses and extends compresses and extends almost like a caterpillar moving the dreaded motor effect how fun so a teacher is demonstrating the motor effect the motor effect is essentially when you have a current carrying wire that's affected by magnetic field field it begin to rotate which fair enough or if you have an alternating magnetic field it causes a current going through the actual object causing it to rotate either way generator motor effect it's the same thing just depending on if you provide the current or you provide the magnetic field the equipment includes a permanent magnet which is this big uh c-shaped thing horseshoe the copper Rod remains stationary when the switch is open cool the tendency for an object to remain stationary is called again memory inertia inertia is essentially how difficult it is to accelerate something so normally something that's really heavy has a lot of inertia because it's very difficult to get it moving and very fun right now when the switch is closed the copper Rod accelerates in which direction will the copper Rod accelerate okay so basically down right up or left so let's go back here when we draw the magnetic field lines what's going to happen so magnetic field lines go from south to North so I'm going to draw those now and what about the current well the current don't forget is the direction that positive charge goes it's not negative charge which is very annoying or it's in opposite direction to where electrons go so electrons are going to be going this way so they're going to be going along down this way whereas r current which is in the opposite direction is going to go backwards right so we have current going to the left we have the field lines going up so we can use Fleming's left hand rule to find the force remember Fleming's left hand rule you have force in the thumb the first finger is your field lines and C is the the C is the current and the current is um your second finger over here so I realized here what I'm going to do is actually has changed the color of some of these so with the current I'm going to draw in a different color just it's quite hard to see the current is going to go in the opposite direction to electron so it's going to go away from the positive so that means it's going to go kind of out of the page and we're going to use Fleming's right hand roll so the thumb represents Force this is what we're going to look for the direction that my thumb goes the first finger is the field lines which go straight up at the moment and your second finger is the current so if I do that from my perspective my thumb is going to the right I'm aware it might be looking that it's going to go to the left for you guys but again if you try and do this now as well it points to the right so for me my thumb points to the right which means this copper Rod will accelerate to the right again I'm well aware that it might be reflected because I think either my camera or the software itself reflects it but again second finger's pointing towards me my first finger is pointing straight up so my thumb is pointing to the right because of Fleming's left hand sorry Fleming's right hand rule so explain one way the teacher could increase the acceleration of copper Rod there are loads of different things you could do um you could increase the current that's probably the best way to do it increase current um to increase resultant Force because remember if you increase resultant force that means because of Newton's Second Law you'll increase the acceleration of the object the magnet used in the demonstration was a permanent magnet figure six figure six shows an iron bar and a permanent magnet describe how the permanent magnet can be used to test if the ion bar is also permanent so a permanent magnet means that it will have a north side and a south side that do not change so what you would do is you would bring the same side the same side of the iron bar close to both sides of the permanent magnet if there is is a repulsion to either side of the permanent magnet then the iron bar is a permanent magnet as well that's how you check so for example if I bring again you won't know if they're North or South yet we bring one side and let's say it happens to be North it will be attracted to the South side and it will repel the north side now the reason why you can't just see if it attracts is because ion is magnetic which means ion will be attracted by a magnet regardless but if it's a permanent magnet it will repel from one side and not the other whereas just a normal iron bar will be attracted to either side of the magnet and so you wouldn't be able to tell through attraction alone this is actually quite an interesting question so figure seven shows a magnetic compass used by walkers explain how a magnetic compass provides evidence that the Earth has a magnetic field now the interesting thing about a magnetic compass is if we think about the entire world let's say the top is the North Pole and the bottom is the South Pole no matter where you are a compass will always Point North it will always follow the field lines and the reason for that is the field lines go from south to North so it doesn't matter wherever you are on the Earth Earth whether you're in the Southern Hemisphere or in the northern hemisphere your compass will always point in the same direction which is the North Pole so to explain this in words the compass needle always points in the same direction because it always points in the same direction it implies that we're inside a massive magnetic field magnetic field that's so large that it doesn't matter where I am I'm always facing the north Direction which is interesting the reason why this happens is because the needle aligns itself with the Earth's magnetic field if there is a smaller magnet close by then you would be able to walk around the magnet and your compass will point in a different direction every time it'll always Point towards the source of that magnet but it whereas in this case it always points in the same direction because it's a massive magnetic field that we're talking about figure eight shows a garden chair hanging from a spring that looks dangerous but fair enough which of the following describes the relationship between the weight and the extension of the spring now whenever here's how I would approach this it talks about extension of a spring think about the equation that you know which is FAL K or KX which is Hook's law okay so the second I saw that was a spring and the second I saw extension at thought of hooks law now the thing is this says F K and E whereas we've been given W and e but what is weight weight is a force so in this case weight equals K so in other words weight is proportional to e so it's not approximately equal it's not less than it's not equal to it's proportional to because it's Times by The stiffness constant right it's Times by this value so it's not the same as once again we can actually use the equation that I literally just me mentioned f = k e and we want the spring constant so K is equal to f e now there is one one other thing one other thing that we have to think about which is this unit here this is in millimet spring constant has to be in met so 60 mm is equal to 6 cm / 100 you get 0.06 M so we're going to do Force 750 over 0.06 to get our value for spring constant it also tells you the units down here Newtons per meter so you can't have millimeters you have to have meters so let's see we got 750 over 0.06 gives me 12,500 again this is a reasonable value I know it seems massive but if you think about it you want something very stiff if you're going to like trust it you know trust it enough to sit in it it needs to take a lot of weight the manufacturer of the chair tests a new spring to see if it is suitable to hang the chair a new spring to yeah cool the spring can store maximum energy of 1,800 Jew before it becomes inelastically deformed what is meant by inelastically deformed let's break down the word deformed means you've changed its shape inelastically is the opposite of elastically when something's elastic what does it mean well think of a rubber band or a spring if I change the shape of a spring or a rubber band so if I stretch a rubber band or if I compress a spring and I let go what happens well I've changed its shape I've formed it but because it's elastic when I Let Go it pings back to its original shape so if you stretch a rubber band you let go it goes back to its normal shape the same is true for a spring so we're talking about the opposite of that we're talking about inelastically deformed that means when we deform it and we you know let go it does not return back to its original shape so um when the force is removed when I say Force again it could be my hands pushing it it could be a weight could be anything when the force is removed the object does not return to its original shape if it's inelastic if it's elastic it does now it says here calculate the maximum extension of the spring before the spring becomes elastically deformed well first of all we need the equation sheet the one you're looking for is a half sorry e equal a half k e s yikes okay you could rearrange this first if you're mathematically inclined if not I would substitute the values in first so 1,800 equals a half K was 225 e^2 so again you can use a calculator but half of 225 is 112 .5 I'm going to divide by both sides by um 112.5 to get e s so e s equals that or you could go straight to e and say it just equals the square root of 18800 over 112.5 so again regardless of whether you're good at the algebra or not you can can do questions like this you just take it nice and slow step by step and use that math knowledge that I'm sure you have and if not you need to watch more of my videos four well that makes sense actually it's four M 4 m is a lot to put it this way someone that's 2 m tall is like 6' 3 or so so that means you have to stretch the spring by like two times the height of a human being before it becomes elastically deformed which if you think about a chair that will be stretching it by quite a lot so I think that's fairly reasonable to have as a you know a seat right surely surely evaluate the suitability of the new spring to hang in the chair um okay so they give us a lot of information here I I would normally highlight it but literally every line is a useful piece of information what I would probably do is is I would work out the extension that happens with this uh chair and then work out what happens um yeah so I'd work out the extension that happens in this case and see if it compares to 30 cm or not right because if it's bigger than 30 cm it means that you know it's totally fine because it would extend and it would will be okay um but again you don't want the spring to extend and then you touch the ground cuz that defeats the purpose of hang a hanging chair right so if you sit in it and he just drags on the floor kind of pointless so you want the extension to be less than 30 cm so let's do that so we have FAL KX now why am I using sorry K why am I using that formula well the 1800 thing is fair we could use that but I want to work out the extension so I'm going to use this formula so we have 750 / 225 which is 3.3 occurring isn't it yeah that's in meters whereas this is 0.3 M so I would say not suitable and then give a reason why not suitable and the chair would basically drag along the floor when someone sits in it in fact the actual mass of that person's only about 70 kg um that's actually crazy that really is crazy um yeah so because basically the extension's too big right if you're 30 cm off the ground you want your chair to extend maybe 10 CM or so 15 cm but if it extends 3 m you basically just go you hit the floor so if we go back to the original diagram this person when they're sitting in it the chair is actually going to be hitting the floor and so their legs will just be touching the ground and it's like what's the point in having a hanging chair if it's not hanging so that would be my argument against it and on to I think this is the final question one of the last questions so far I don't think this has been too hard to be honest um maybe the conclusion question that we just had now but yeah a charge dropping a stone into the water when the charge drops the stone it passes the charge feet with a velocity of 3.1 the charge feet is 6.3 m above the water so from here to here acceleration to gravity 9.8 calculate the velocity use the equation sh okay the equation you're looking for is v^2 minus I just realized I'm not using the a version of this minus u^2 = 2 as s so that means v^2 = u^2 + 2 as s that's the a level version then we're just going to sub in the values so v^2 equals 3.1 squ remember U is the initial velocity two acceleration is 9.8 s is the height traveled 6.3 M and then all we're going to do is square root the answer afterwards for four marks man to 2 SF that's crazy um yeah I just love you know just love the calculations here I understand that I might be I'm on the minority there and then just Square answer and we got four marks 11.5 but it says to 2sf so that would be this second uh digit so we running it to 12 four marks lovely absolutely wonderful velocities of vector describe the velocity of the stone as it falls through the air they've done you a favor by reminding you of this because what is a vector compared to a scaler a vector has size and Direction so in this case we're talking about the speed How does the speed of the stone change and how does the direction that it's traveling in change so start with the speed well the speed or magnitude whatever you want to call it or size increases you can leave it as that but if you want you could say constantly or uniformly but just saying that it increases is fine and the direction remains constant it's falling downwards right when you drop something it doesn't like zigzag around right it drops straight down it doesn't ping left and right and go up and down it's just straight down so the direction is constant it's constantly going downwards but it's speed the size the magnitude whatever you want to call it increases you can say constantly if you want but that's not required for for the mark scheme figure 10 shows the stone just after it's entered the water as the stone moves to the water the stone slows to a constant velocity I.E terminal velocity explain why four marks well let's talk about this shall we um initially as in as it enters the water the drag is greater than the weight this means that there is a so therefore resultant Force upwards which causes a deceleration in other words it causes it to slow down now as velocity decreases the drag also decreases when drag equals weight there's a velocity constant velocity essentially when it initially hits the ground the ground the water the drag is massive because it's moving very quickly so the drag is really really high the drag causes the stone to slow down now as it slows down the drag actually decreases until we reach an equilibrium between the weight and the drag where it will move at a constant velocity now we're on the final question I totally didn't get that wrong a car contains a device called a black box the Black Box records the velocity and acceleration of the car the car was traveling at constant velocity then reacts sorry then the driver reacts to a hazard the car doesn't and they you know slow down to zero because they don't want to like kill the child or whatever it is that's right in front of them determine the deceleration give the unit when you have a velocity time graph deceleration is simply the gradient of the line so let's do this let's do the difference in the velocity so it starts at 26 and goes to zero so we're going to do 26 and we're going to divide it by the change in time so they start decelerating at 2 seconds and they stop decelerating at 5.1 5.2 525 if I actually get rid of that cuz that was stupid at me yeah let's say 5.25 so we're going to divide it by the difference between 2 and 5.25 so 5.25 minus 2 so 3.25 I could have probably just done that but you know what I want to be kind to myself um and we get eight so the the acceleration was eight or the deceleration and the question is what's the unit you can get it from the actual question says m/s per second so in other words m/s squar again three marks man beautiful beautiful it's quite an annoying question uh five Mark calculation fairly Hefty the driver of the car has a reaction time of 75 seconds determine the stopping distance of the car now the stopping distance is the distance the car travels before it stops I know crazy right now the key thing here is that there's two components to it the first one is the thinking distance this is the distance the car travels before the brakes have been placed so the Danger's there it takes you a second well in this case 0.75 seconds to react in that 0.75 seconds how far does the car travel that's essentially the idea plus something called the breaking distance so this is after the braks have been applied how far does the car still travel now there is actually a shortcut here the shortcut is you could just work out the area underneath this graph because the area underneath a velocity time graph is the distance but whatever right the thinking distance here is just going to be the area underneath this initial part or in other words it's going to be simply um in fact let's remove that there we go it's going to be the distance traveled in that 0.75 seconds now as we know speed is distance over time so distance is speed time time so the speed that the car is traveling at before it applies the brakes is 26 m/s and that is for 0.75 seconds so let's do that first so 26 * 0.75 that should be like 19.5 or something like that whoops 26 * times 0.75 gives me 19.5 m and the breaking distance is now the basically it's just the area underneath the Triangular part of this graph so again the first distance you get from doing speed times time because it's that 0.75 seconds and the last part is just the area underneath this because the brakes have been applied so this is a triangle the height of the triangle is 26 the width of it is 5.25 minus 2 right cuz it goes from 2 to 5 .25 so let's say it's 3.25 and then we times it and divide it by two so 26 times damn it I've already F 3.25 man I need to I need to get my brain tested I'm divide it by two so let's do that I'm well aware my handwriting is a bit sloppy at the moment 26 * 3.25 equal / 2 G gives me something went wrong there 26 * 3.2 oh I see whoops press the zero instead of the decimal point key 42.2 and then all we need to do is add them together to get the stopping distance so the stopping equals 19.5 plus 42.2 which gives me something so plus 19.5 gives me 61.75 m and if you actually think of that distance for a second that's a really long distance if you think about 100 met race it's over half that distance just something to consider for when you eventually can like drive and stuff let's go on to the last part of the paper I honestly don't think this paper was too bad overall um but honestly this is a really hard calculation to do if the Black Box records large decelerations it identifies that the driver may be dangerous explain why large decelerations may be dangerous well honestly there are so many things that you can say here the first one is that the brakes overheat um overheat that's one Mark so they don't work properly that's the second Mark another thing you could say is can lead to loss of control again the second Mark here is because the tires lose traction um and lastly bigger deceleration means bigger Force that's one Mark and the second Mark is large Force leads to injury um any of those is completely fine again they come as pairs right so you need to say both things to get both of the marks um yeah that brings us to the end of paper two hopefully you found that useful if you have again do consider subscribing do consider going to the my website or to the email in the description and you know checking out if you need tuition or something but I will leave you to the rest of your revision and I'll see you in the next one