We got number five. The boy sits on a box in the left. Master, the boy is 45 kilograms. The master of the box is 20 kilograms. Master, the left is that's was a 50. To Bogot both on a box in left, okay, lift is being raised vertically by a vertical cable which is attached to the top of the left. Nice little diagram, lito. Move it upwards. Constant deceleration, 2m per second per second. The moin, the cable has been light and extensible for intenin. The cable, the mature of the force converted on the box by the boy, the maitde of the force exerted on the box by the lift. Okay, so we've got our diagram. We had any forces to this diagram. 嗯，the maybe maybe. A little bit bigger maybe now it's bit to like to squish. Yeah, good, but bigger. Oh, I can't really draw, so I do stick. That's good. That's all it needs to be. Lovely stuff. Okay, so this is go again. So the force, so sorry, the way of the boy is 40 5G good. Lois Newton, no, that's a the box that's. The box. So that's 20G Let'S G from the box yet. So then the whole do you say how having the liis Oh Yeah, it must the left 1050 1050. So the whole okay and then the lift is. Then the whole thing like the whole unusual, like should we do the whole thing together? Like Yeah. So so this is this is when this is a very vague noand start law question because obviously the boy is pushing down on box. And then through Newton's third law, the box is also pushing back on the boy. Otherwise the boy would fall into the box. The box is pushing down on the left and the left is pushing back up on the box. And again, they're equal, otherwise the box would fall through the left. And then we've got the whole thing being pulled up. So we've got a tension up here as well. And we have acceleration as well. I will tell the acceleration, I tell me, Yeah. So we're moving upwards. But with decelerating. So that means the acceleration is in the opposite direction to motion. Happy with that. Yeah was it's moving lift is moving up. Yeah, Yeah, moving up, but it's decelerating so the acceleration is acting down. Okay, okay. And then for these questions, it was a bit like the connected particles one before. We've got a choice of what we can look at. We can look at the system as a whole, which is what we need to do. Pi, that's what you said. But for part b and c, what we'll have to do is we'll have to look at individual parts of the system. So in this system, there are three things. There's the the boy, the box and lift. So we've got choice. We can look at just the boy, we can look at just the box, we can look at just the left, or we can look at all all three of them together. So part a, we can look at everything together. So what we're gonna to do with that. We add the so the total force is. Sorry my. And then why turn 50? We sorry not 250. Up 11 zero five. Ky 11 zero five. Because 1050 ad 65 is 11 zero five. Sorry, no no no, I not. It's one wait isn't not no, it really. 1115, 1115, Yeah. And then ecourse. T minus I'm fact g with what I'm so confused, f equals because it's going upwards. Yeah the resulting force must be like, so t must be bigger than the weight, right? Yeah. So the resultant force is not always in the direction of motion, it's in the direction of acceleration. Sorry, 1s. It's moving up. It is moving on up slowly. It's decelerating. So it's not just it might be going really fast, but it's slowing down. But it's slowing down because the tension isn't as high as the weight pulling it down. Okay, so the tension is going to be smaller than the weight, but if the tension is not bigger than how is that going on? Because it would have been bigger at some point. I'm still where you can be used, sorry. So the lift, what happened? The lift would have stopped, the doors would have opened, the boy and the box get in. The lift closes. Happy with that. Yeah Yeah. He's then pressed the button on the left. He's gone up somewhere. So he's pressed that down. Flop five. The left is then start to accelerate because it has to accelerate because at the moment it's stationary. It's then moved at a constant speed for a bit. And then as it gets close to his floor, that's when it will start to slow down. Okay, so we're looking at that bit. We're looking at that bit of motion where it starts to slow down. So we know it's slowing down because we've got acceleration down, but motion is up during that. The tension, the force pulling upwards has to be less than the force pulling it down, otherwise it wouldn't slow down. Tengetting, but Yeah, so at this particular point, it's constant because we've got constant deceleration. But yes, tension, it has to be smaller than the weight for it to be able to slow down. Okay. So it should be minus two then. We know we comyou so we can go minus two if we do t minus the weight, the resulting force, or we go positive to, and we do the weight minus two. Essentially for your f equals na, you do it in the direction of acceleration, okay? So we're looking for the resultant force in the direction of the acceleration, okay? So if we wanted to, we could do we could do this and go, we've got an acceleration upwards of minus two and then you could do two a minus two times and then it would be t minus Yeah because we want the resultant force in that direction, in the same direction as the acceleration. Okay? Because f is a vector and a is a vector. So they both have direction. And because m is just the scale, they have to have the same direction for that to work. Okay. Okay. So it's a bit like with the with the suequations, it doesn't matter which direction you pick as long as you consistent throughout the whole question. Okay, so wherlike the it's traveling. So wherever it's traveling, it has, it's like the force on the hand says traveling to minus the force on the opposite end. So it's not the way it's moving, it's the way it's accelerating that you're interested in. Okay, so so this this catches a lot of people out because they go but theydo similar things to you and go, well, it's moving upwards. So tears to be bigger. And I agree it is moving upwards, but it's slowing down. And for it to slow down two to be smaller. Okay. So as long as you do your resultant force in the direction of acceleration, it doesn't be fine. So. Set your overall force downwards. Oh Yeah, sorry. Just there's so many things that you have to remember for these kind of questions. All that. Okay. So the tension is 8697 newtons. Technically, we should round that to two significant figures because we can't be more accurate than two figures, but that's fun. Okay so part a Marks but Oh sorry no no I know. Oh, I was going to ask if you don't around to like a specific amount significant because where they take Marks off neither, right? No, it would just be in the mark scheme. This won't be the actual answer. It would be it will say something like answers which round to 8700. Okay. Yes, you're not wrong that, that like that is the answer for these numbers, but you can't technically, you can't state that as the answer because that is too accurate for the data we've got. Okay, but now that's fine. Okay. So with these questions as say you're always either looking at whole system together or individual particles to pa is usually the whole system together and we have to use the whole system here because tension is affecting the left. So you can't really just well, we could look at just the left, but there's too many unknown forces in the middle. Okay, b and c, we've now got a choice. We have to pick something else. So we've got pub mounted of the force exerted on the box by the boy. So we've got the box and the boy. Who should we look at or what should we look at? The box or the boy? Why, okay? Why the boy? Excuse me? Oh, bless you. I'm sorry. Yeah, good and good. So why the boy are not the box? Because the force exerted by the boy. Okay. So what if that said the force exserted on the boy by the box? Would you then look at the box? Oh, my gosh. And went exsearon the box by the boy. Do you have to look at both box and the boy? No, because of nationsaad law. Oh, so you look at the ducbox. So every force has an equal and opposite reaction. So whether that was on the box by the boy or on the boy by the box, the question is the same, okay? Because they're the same value. So we want to look at the particle or the part of the system that is easiest to do math with. So do you reckon the boy or the box has less forces acting on them? Oh, my gosh. The the boy has less force, acted brilliant. Yeah. So another rule in these sorts of questions where things are stacked is you never want to look at the middle one, okay? Never consider the middle one by itself. So it's always, it will always be the boy, whether that says box on the by the boy or boy by the box, okay? The reason is the boy's got less forces because the box has its own waist. He's got a boy pushing down and it's got a lift pushing up on it. It's annoying. But boy, he's only got his weves in the box affecting him. Okay. So in part c, do you have a look at the box on the left? The the lift Yeah the lift because again, we don't like doing the middle one because the middle one's hardest, okay? And the order of these two words doesn't matter because of Newton's third law, okay? If you work out the force of glasses on the box by the boy, it's the exact same as the boy by the box, other than the direction is the opposite. Okay, so what I encourage you to do now is draw another diagram for just the boy. So if we scroll down, I'm going to Press that one. So that was me. Brilliant. My lines don't come with it. Why don't they move with it if I do that? Nope. Okay. Those lines are staying there forever, I guess. Okay. So let's draw a diagram for just the boy. So what we got. Boy. In the box. So. We don't even need the box, actually. We just look at the boy. So what does the boy feel? Il, you know, we don't, we don't even care about the box, just the boy. Imagine you're that boy. What forces are acting on him? Like the reaction? Good. Yeah, there's a reaction force holding him in place, otherwise he falls through everything and then what else? And the way wait, Yeah, that's it on the boy. Sorry. And the way. Okay, Yeah. And the way, and know that's it. The two forces got his weight downwards. We've got some reaction force pushing him upwards. Yeah, and we know we know his weight because we were told in the question. Lovely stuff. Go about acceleration. Is the boy accelerating? Yeah, Yeah, he feels the same acceleration as the lift does because he's in the lift. Good. Yeah. So it's up with minus two. Lovely. Okay. If there's no acceleration, the weand, the reaction force are the same. You happy with that? Very that please. So if the lift wasn't moving, if it was stopped at floor five where he's getting off, are you happy that the reaction force from the box will just be the kiwait theybe the same? Yeah. However, because he is moving or no, because he is accelerating, it's going to be different. Okay. So we're expecting a number higher or lower than the boy's weight based on the minus two acceleration. When expecting it to be lower. Good. Yeah be lower because the way I like to think of it is you know when if you have been on liand, it moves up and you sort of feel yourself like be pulled downwards, but you sort of like, Yeah. So that's because the lift is accelerating up. So this is the opposite because it's decelerating. It's gonna to feel briefly a little bit lighter because this will be smaller. So I'd always have that little thought in your head just to go like I'm expecting an answer bigger or smaller than the weight. And then it's just it's just the same matter as we had up here. So it's eals ma again. But instead of having the resultant force be based on the whole system, it's now just based on this. Okay. So we've got some reaction and then we just find out we use f equals ano, use newison second law, and we find it sorry. Oh, sorry. I was gonna to ask with them the is just 40 pe yes just the boys y's brss Yeah because we're just looking at just the boy. Okay. Then it's with the I'm confused what so f. Is minus two times 45, which equals to. Our minforty five. Is that right? Yeah, exactly that. Okay. Yeah. Oh, okay. Okay. And then we get a reaction that is so based on this, we're going to get a reaction that is 90 below 45. Okay, Yeah. So we get answer smaller. That's what we're expecting because he's decelerating and then because of Newton's third law, even if this question says box and boy the other way around, it's the same force because of Newton's third law. Okay, so what is R. Let me. Three, five, one, that's what I got, 351 stuff. And we got an answer smaller than our, which is what we were expecting because it's slowing down here is the reaction force doesn't need to push as much because he's decelerating. I mean, said when a person goes up, the person should feel heavier or like, so again, it's, it's it's it's weird because everyone wants it to be ID to do with motion. It's not to do with the motion. It's to do with the acceleration. So if he accelerates up, then Yeah hefeel feel heavier because the reaction force would be pushing up more than his weight. You know, that's why in the lift, sometimes when it first starts moving it and it starts to accelerate, you sort of jolt downwards a bit because you can feel it pushing you down. But what if you go down? Like so if you're in the limoves down? Yes, when it first accelerates down, you'll feel a bit lighter because that the lift is like falling out from under you, if you like. And then as it starts to slow down, but it starts to decelerate moving downwards, that's when you'll feel that floor pushing up on you and you'll feel heavier. Is that the same if the person's like in the sethat's kind of different right in the sea? What do you mean? Like because I know because you don't water I kind of give you like resistance or something Oh like Yeah Yeah Yeah. Yeah, Yeah same same if you're in water and you have instead of a reaction force you've got that up first us Yeah Oh okay we sent so then was up thrust up thrust is just like the reaction force of water if you like not quite because you're in the water and not like on the surface of it. But it's the upwards force in a liquid. But then are we ignoring like when am I doing all this? Are we ignoring like air resistance and stuff? Yeah, air resistance doesn't exist in this matunfortunately. Oh, so it's not it's not that it doesn't exist. But we model particle, we model objects as particles, and particles have no dimension. So even if there is air resistance, they wouldn't feel it because they're like infinite, infinitesimally small. Yeah essentially essentially we ignore our resistance. Yeah, okay. Admittedly for a lift, there's not going to be much air resistance anyway. In fact, the boy's not going to feel any ersince anyway because he's in the lift and he's not moving. The lift will hit a bit of air, you know the bit a bit of air resistance, but lifts don't move that fast anyway, so it's going to be negligible. Yeah okay. For this question, just to tie off, I would say in which direction this 351 is going. Just for this question. So the force goes, Ted, on the box by the boy because technically we've worked out the force exerted on the boy by the box. So here our 351 is going up based on our diagram, but we want the puse exsted on the box by the boy. Yes. So I would just write 351 newtons downwards for our answer, okay, because our diagram is currently saying upwards. That's because we worked out the opposite of what they've asked for. I wouldn't write it there though because that technically you're saying it R is going down. I'd write it like again, like here essentially just to go like like to answer the question if you like, because R is going upwards. Our reaction. Okay. See, you don't have to write the full sentence. You could write the force exerted unbox xed by a boy just three, five, one down. Just just to make it really clear that you understand the newtonan's third law that they're the same. Lovely. And so here we've made luof nuisance third law because we actually didn't find out the force of duon the box by the boy. We did the force exersted on the boy by the box because the matter is easier. Okay. And now part c, we do the same thing put for the lift. Okay, okay. So we look at just the left. So we need another diagram for the left. So wehad the writing to the move with the picture is only not the picture. Yeah, no, isn't it? I wanted those lines to come with it, but they just didn't. But if I have a bigger document than it does, so you know that when we've used like the textbook pages, Oh Yeah, that stays in it for some reason. I don't I don't understand. All right, we've got a left. What does the lift feel? So where's the reaction coming from? Sorry. Wait, no, no, then the reaction is coming. There's nothing underneath the left. That's coming from here. Right? Okay, explain explain that. It started on the box by the lift. Oh, sorry. Yes, but we're interested in the forces exerted on the left. So what does the lift feel? You are right. There is a Yeah, there we go. The sum falls downwards because there's stuff in the lift. Yeah that kid in that box will tell if the box is exin the force alls, but the kid on top of the box are pushing down on the left. Are are there any other forces happening on this left? On this lift, Yeah, there's lifeel anything else? Tension lovely. So a bit hard enough for the left because there's three forces instead of two, but the mast is going to be exactly the same before we're using Newton second law. So f equals ma. And then at the end we're using Newson's third law to go, Oh well, it's this force burn in the opposite direction. We work out I think we worked up tension already. Yeah we new tension actually question one we've got tension. There is 8697. 8697. Wait. Then the F, I made, then the m. Is that still one, one, five? No, it's just the left. So we're only looking at the left. The weight of the kid in the box is taken into account with the reaction force pushing downwards. At minus. Oh Yeah, sorry. Is it? One, two, five, ten or 500, that's not what I got. I've got 3000 in there. Let me try again. I think it's me. 8697 minus ten 292 is that. No, I think Yeah happened. You're right. 507 lovely. And if we if we think about the whole system again, so we've got the kit ID in the box they should because it's decelerating, they won't be pushing down on the lift as much, which is why that 507 is below there. Their overall weight set the kid in the box of an overall weight of 60 5G. We've got 507, which is like, what, 51g. So it's a bit it's a bit below, which is what we're expecting. And then again, I would just finish it up with a sentence to go going you to the 46s and the box by the left. Is that in which direction? The y is like this one, the same, like the y is all the same, but opposite, not again, sorry. And White like here, like the acreaction pair is like the same. So why they're the same in the Yeah but like why is it like in the other calculations, we have to think about the acceleration. So is it big back? Sorry, should we go to that? Yeah. So it's same in this one. It's just it's always epic als m essentially. So we still use the acceleration in both cases, but we've looked at each we've looked at individual particles instead of the whole system. Okay, if we wanted to we could look at the box but you never in a position where you need to look at just the box and the box is nastier because the box will have so the box has its weight down. It's got a force by the child acting down and it's got a force from the lift pushing up. So if you wanted to, you could check with the numbers we've got. But but there's not I wouldn't say there's a need really okay, see in gentlemen, that's right. Yeah, you just mind it. Yeah, okay, you got it. Yeah, it's just like my pen. Actually, I'll put the next one in. Are you happy with that? Yeah. Yeah, sure. Yeah, Yeah. Let's go down then. Well, I think that last one was also I think it's quite similar. We've got lifter sends with an acceleration of 1.5 who's at a constant speed until tilties. So that is see what and is a constant speed until it is decelerated. Okay, extra matwenty K G stands on the floor of the lift drithe journey. And the magnitude, the lift at each stage and the journey. Okay. So there's three bits to do for this now. So what should we start with? A diagram. Yeah, sure. And then a package. And the magnitude of the force it exerts on the floor. Can you see we've got three stages, so it's fun that force examine the floor at each stage. What's the third state? So there's the acceleration, there's the constant speethere's, the deceleration. So the constant speed eds, a really easy one. There's not really any matths to do for that. Do the two bit nastier. Okay, okay. So this is our diagram of the system overall, because we want the module of the force it exerts on the floor, we have to look at particles separately. So just like before we got a choice. Do we want to look at just the package or just the left? Okay, why the left? Because this smaller force exaction left sorry, smaller forces exhasted on the left. Okay, let's draw a diagram for just the left. So what does the lift fail? It's fair with apostit this one. Yeah, we can just use this one. Oh wait, we don't know the MaaS of the lift but we don't have to use a box. Brilliant. Yeah, okay. Also we don't have the tension so we have to use the box as well. Okay? Although be fact, if we knew the MaaS of the left we could have watched out the tension like we did in the other question. But Yeah, this question is going to be a lot easier the package because we already know it's MaaS and we don't need the tension. That's cakes. We only care about the package now, so we don't actually need the lift. Yeah, good. So it's got its MaaS, not it's weight, pulling it downwards. Does anything push it up? Yeah, good. So it's it's the same force diagram for all three stages, apart from the fact that the acceleration is different, so your acceleration arrow will change. Okay. So that's which stage should we do first? The acceleration of 4.5 okay. Yeah, good. Now it's the exact same as the previous couple of questions. Sorry, I'll just scroll down on you there. Lovely yes f equals n. Good. Then what is that? That's what I got. Yeah. And again, that that makes sense. It's accelerating up. So Yeah, we're expecting the number greater than the weight. And we did and then we do repeat that for the other two accelerations. Okay. So stage two is constant. Once constant, just is it just like the same aptitude as gun g? So what? 196? Yes. Yeah, good. Because constant speed means acceleration is zero. You can use this equation it's the same. It's just that there's no results force because the acceleration is zero. So Yeah you can Yeah for stuff and then stage three I think it was we'll it one deceleration of one. Good, well remembered. Yep. Yeah, that's what I got. Good. And then in that case, we're expecting a force, but it's smaller than the weight because it's decelerating. Yeah, good. Brilliant water. Okay. So the trick for the newters third law, there isn't really much to it other than when it says. So the that was awful. Of course, it exerts on the floor the left. We can either consider the left or the particle depending on what makes our life easier. So sometimes it's easier to consider particle, like in this case. In another instance, though, it might have been easier to look at the left depending on what info they give us. So if they gave us the MaaS of the left and say the tension didn't give us the MaaS of the particle, then it would have been easier to look at the left, okay? It's just remembering that, okay? They are like they're the same essentially okay to these ones as well. We don't need to give a direction because it only asks for the magnitude. So I don't I don't care out which direction they're up now. Okay, this one that we did earlier is is a really, really common exam type one where there are like two particles within within a lift or theyhave two particles on like a like a scale, like a measuring scale. And they really like those ones. And essentially it is just ignore the middle one. Okay? Look at the whole system. Look at the top particle, look at the bottom thing, hold and everything. Okay, happy with that. So that make a bit more sense now. Yeah, it makes much more sense now. Brilliant. Well, that was the last one we had to like. Yeah was the last one. We've gojust there ten minutes. What are you feeling? Do you want to another one of these? Do you want to find one of these and do another one? I think I'm okay. Okay, yes, we start the next thing to prefair. Our next lesson I think is only thirtieth so it's not long to wait. Yeah so we could just start we can do like Oh Oh Yeah maybe or we can do like another kind of corner Polly questions. Sorry, like police at the corner. Holy up. At the corner like a table. Oh, pull. Sorry, our miss here. Yeah. Yeah, we may. I'll find a poly question. We textbooks not loading, give me a minute, my textbooks being stupid. There you go. So what we've got box paid MaaS 2.5 klograms rests on a rough horizontal table attached to one end of a light in extensible string shrink pasover a small smooth pulley fixed at the edge of the table. Other end of the string attached to a sphere. Cuue MaaS 1.5 kilograms hangs freely below the pulley. The bantude at the frictional force between peand the table is k newtons system is released from rest with the string torque after release cudescends a distance of 0.8m in 0.75s, modeling them both as particles. Calclick acceleration of q show that tension is that find the value of k and then b state. Having your calculations, we use the fact that the string is inextensible. Lovely stuff. Okay, so this one is going to cross over a couple of topics, actually. So what should we do first? Just use super Yeah brilliant Yeah part part a part one has to be super Yeah. Below. Oh, wait, no mind. Oh wait, that one other thing we know. I'm sorry, I'm trying to underline and it's just moved over these from rest. Okay, so that's zero. Brilliant. There you go. So which way you said is positive? You saying down is positive? Yeah Yeah Yeah I Yeah because of the point a, that's fine. Okay, I would always make a note of it just so you know. In which like just to keep track of it essentially, however, in this question doesn't change anything because you'll get a pause today. Okay. Which which equation are we using? Wait, is that? S equals U square red plus a half 18 ut. It's fun that they're in the formula book. You're not actually expected to know them. Let me. Plus I have at squared yes s equals ut plus a half at squared then Yeah plug on numbers in. Oh, that is 0.75 squared. Not a nice numbers. There is about 2.84 what I've got. Lovely. And part two show the tenin, the string is 10.4 newtance. Okay, now we've got some some forces stuff to deal with. So how are we going to find the tenature? I'm not sure if you can hear my cat. Sorry, but I'm really sorry. But Yeah, just briefly that I did. Yeah. A pension of. The resultant force is. Yeah, we can. Really do with a diagram now, can't we? Oh Yeah, Yeah, Yeah. You could probably edit this one up here. Because that's got everything we need, isn't it really? She's going to change that to a little. I got Yeah. So it's moving it's accelerating this way. Yeah. So Yeah because the PaaS has falling, so it's accelerated downwards. And then which way is particle p moving accelerator? It's going that way. Yeah with the same acceleration. Yeah. Yeah, good. So we want the tension, just like in the lift questions we've got. We could look at the whole system. We could look at individual particles. What do you think we should do now? Yeah, so actually, I made a bit of a line a bit there. You can only look at the whole system together if everything's moving together. Okay. So for this one, we can't for the pulleys, you can't usually consider the whole system because one particle p is moving to the right and q is moving down. Okay, Yeah, we've got any forces on our diagonal. We should have. That's one point 5G. And then I'm not sure if necessary. Oh yes, that's 2.5. Yeah, I'm missing one, two, three, four forces. There's one more on q and then there's three more on p. 11 cuyeah more lovely yet attention. Touch Ching that Yeah suppose there's two on the pulley as well, but we don't care about the pulley this time. So what else has happened to pay? I'll something to be. Is a resultant force us not resulting for us? Oh, friction and force. Sorry, brilliant. Yeah, there's friction and then there's the reaction. Okay gooyeah, they call that k and then there's a force from the table pushing this upwards, isn't it? Oh yes. Yeah. So for at the moment in year year one mechanics, friction is always given to you as a constant force like this. They said the friction is okay because they haven't actually given us. We've got to work it out. But in year two, they introduce friction as so friction is something to do with R. So later on you'll have to put this R on and this the weight on because theybe used to work out the friction. However, in this case, those two technically aren't needed. Okay, okay. So now to find tension, we've got this f equals ma. Again, we've got two particles. Which particle do you recwe should deal with? Yeah, cube. Because there's two forces action on cube. And we know one of them. Yeah. When you type it in, use the exact value you got for a just so we don't lose any of our accuracy. If you had it as a fraction, that would be good. How to do that? Like on this to calculate? Do you know how? Because is it does it not keep it as a fraction? No, it doesn't. I think it's some about some kind of like math load. I just can't do it. Like I can I can type like I'm not sure. Maybe it's like the other way around if you see it. But if I Oh, and it's too bright, I can't quite see it. Not I don't know. Unfortunately, I haven't got one of those anymore, so I don't quite know how work. I know, but like it's kind of like this, Oh Yeah. And then if I call fraction. Oh, wait, it works. Oh no, that was. Oh Yeah, I just worked out myself. No mind. Now I know how to turn into a factory. Yeah. It would just make it easier to keep track of exact values as all. Yeah, well, I know why I didn't know how to do that before. No, never mind. It's and then. R equals. We get rid of this. We've got more space yeokay, yes. We know. So we're going in the direction of excelthere we go yet. Other the way around, I think and thatwill give you a negative. I now what on about personal attention lower than that's right Yeah that's why Yeah okay Yeah there we go. Just realized I've got the answers on there, so I can check this today. So that's about Oh Yeah wait then that's about. 3.3. Yeah Oh, not 3.3. Oh, sorry, I look at the wrong 10.4. Yes, that's what we're after. That's what it says here. I'm going to stop you there because I've realized we've just gone over time. But Yeah, Yeah so Yeah, brilliant. Part three is then the same thing, but on particle p. Because you then know t, but you don't know. Okay, it's the same maths again. And then quickly, what that be, how we use the fact that the string is inextensible. We've ignored the like the forces on this fray. What do you mean? Like like the I'm not sure, like the I forgot, it's called like the elastic venyeah. Let's imagine the string does stretch. So let's imagine we're using like an elastic band instead when we let go of the system. What would happen if it was like an elastic man that was really, really stretchy? Oh, it was good to go back. It would eventually ping back. Yeah. But what about before that? It. Do that. I know like stretch. Okay, so there's two things that it being inextensible effects. So the first one, the acceleration is the same throughout. Oh, Oh Yeah, Yeah. So imagine imagine if me and you put like a like a Bungie chord between us and I run off in one direction, initially you wouldn't move because the Bungie chord would just stretch and I'd go farther and further away and yoube like, well, I'm not moving. Whereas if we did that with a face string that doesn't stretch as soon as I move, as soon as I get to the end of that string, you've got to move Yeah. Okay. And then the second bit, the more important part, it means the tension is going to be the same. So I know you've marked them as tp and tq, but they're actually the same value throughout the string. Oh, okay. So it's it's a really small word that loof people will just skip over because it comes up in every question. But it's really useful mathematically because it means attention to same throughout the piece of string and acceleration, the same throughout the system. Okay, bottom of that though, I know we've covered some not nice not nice maths there. So well done. And Yeah, I think I think our next one I'll get you down is thirtieth. Okay. I was wondering if we can look some like Pure Math. I'll send you over like the topics. Yes, yes. And know whatever you like. We can have a look at. Yeah. Okay, thank you. Well, then have a good rest of your day and I'll see you in a couple of days. Bye too.