Hello miss. Hello, Jackson. How are you today? Great. Good. So I have some work power and energy questions for us to look at again. And if you want me to do anything on Sunday as in a different topic, let me know. Well, different topic, not yet. I wanna see some exact questions. Okay, so here is a question. The diagram shows part of a roller coaster ride at an adventure park. The carriages are pulled from a to b, has a steady speed by an, an electric motor of power in output, 52 kilowatts at b. They effectively have no motion, no kinetic energy, and they run freely down to c. So the mopushes them up here, and then they run freely, freely down there. The carriage and passagers have a MaaS of 3400 kilograms. How long do the carriages take to rise from a to b? So how long does it take for the carriage to be brought up to b, given what we know? Let me see. We know that the Holthe vertical height, the maximum vertical height is 72m, and from a to b the power output is 52 kilow ts. So the equation p equal to q over t and q Yeah, we do not know the work down. But the carriage and the passage of a MaaS of 3400 kilograms. So we can know that Yeah we can know the time. So I mentioned P O P is equal to W over t and W equal to F S, so equal to fs divided by t so the vertical, so that is 50 diand s. 72 good. It's painting 3000 hundred times 9.81, and then that is equal to 5.2 times ten to the four. No. 72 times 3400 times. 9.81 divided by 5.2 times ten to the four. So t equal to 46.2s. Then they want you to calculate the speed of the carriages at sea. So what will be the speed of the carriages at sea? Speed of courasea. Speed. F V power also equal to the force times velocity. No no, no envy, no not envy. There's an equation about the v about velocity. What is your gravitational potential energy being converted to as it goes down a hill? 5.2. Oh no. Gravitational ational potential energy transferred to the kinetic energy, the highest at this point. Gravitational potential energy equal to mg H. Mg H equal to m. 3400 times 9.81 times 72. The thing is c just be careful c is not at zero height. Yeah. And then mj equal you a half mv square times two divided by 3400. And then this number square root. 36m per second. So the actual speed at sea is found to be 33m per second, not 36m per second. If the track from B2C is 95m long, calculate the average resistior of forces acting on this part of the ride. So. Therebe some frictional force acting on this part of the ride. We can use the relationship here. Work is force times, distance. Which is equal to the change in kinetic energy. So there's some loss in kinetic energy, and that's due to the resistive forces. So if you work out the kinetic energy to give 36m per second, and the kinetic energy with 33m per second, work out the change in kinetic energy. We know the distance. So this is 95m long. We can work out the resistive force. The work is done by friction to reduce the velocity instead of 36m per second. It's 33m per second. So Oh okay. So this difference is because of the frictional between in the track, on the track. Yeah. Okay. So every resistiforce 95 from B2C is 95m long from B2C so the average resistively we know that. So we want to know the fourth force is啊，瑞。So what you can do is work out the kinetic energy. When the philosophy is 36m per second. And the kinetic energy and the velocity is. 33m per second. And then you get the change in kinetic energy, you subtract them and you know the distance, you can find the work done against the resistive force. So. Work. Energy. Essentially, work is done by the resistive force in slowing down the train. So is the change in kinetic energy. So you subtract you work out a half mv squared using that as v, you work out half mv squared using that as v, you subtract them and you relate that to. The force times distance. So a half. Times. Three, four note not. Times 36 squared. He a. Half. Times thirth the MaaS. Times 33 squared. So this is one page five. 13 not north. Genus. This is 217. 8788 juwels. You subtract them to find a change in kinetic energy. So 2178788-18513 zero zero so we catthree two. 74 piece age. Jewels. Is equal to the force times the distance, the resistor force times the distance. So I divide that by 95 because that's the length of this, then off and I can get the resistor force. So I guess the resistive force as three, four, four, seven, three points ins 47. Killing nutions. Okay. What is that it? But why is that? Is three, two, seven, four, eight, eight, juice a half, mv squared a half. So I work out the kinetic energy. What the kinetic energy should have been with no friction. 2178788 jeyeah but the friction with this slower speed, so the kinetic energy with the slower speed is this. Then I us so I subtract those two. And then I take that taaway that subtract. And I get this number divide by the distance, which is 95. So the frictional force is 3417 mutants. Yeah. Okay. Right here is a Sanki diagram showing the power transfers in a car moving at a steady speed of 18m per second along a level road. What percentage of the energy available from the petrol is transferred to the internal energy in the engine, to the internal energy overall? Percentage of available for the pencil arranfor internal energy internal. Internal energy in the engine. So. Internal energy in the engine maybe. So this is the power inpush. Where are the engine losses, the transmission, so the moving parts losses, air friction losses and road friction losses. So we work out what this is, 66 minus three, 3.5 minus six, -4.5, 52, and then divided by six, 66 times 100. 69 sorry 7970 9% good. So osh gets transferred to the internal energy overall. Continenergy. 100, yes, 100% good, because effectively your internal combustion engine is heating up the engine, making the moving parts work due to heating explosions, and it heats the engine, it heats the atmosphere, it heats everything. Calculate the effect of fritional force opposing the motion of the car produced by the air and by the wheels. As air and wheels, so effective frictional force opposing the motion of the car, producing by the car. Remember, we know power. We know velocity. Yeah, power, velocity. And is that power equal to MaaS times velocity, force times, philosophy f, the fourth times. Do you remember when, where this comes from? So were R equal to W equal, equal to work down, divided by time. And work down is is force times distance divided by time. So s divided by distance, divided by time is velocity. So that is fv, fourth times velocity. Yeah. So we're now to what the force is. For air. So firstly the air is the air friction is six kilowatts and the velocity is 18. So three six times ten to the three. Divided by 18. 333 good. And then the queen is in the road friction. Road friction, correct? Okay, 4.5. Times ten to three, then divided by 18. 250. Good. Okay, define work done by a force. So if you see the word define, you can give a word equation for defining it. What equation or define? Okay, define work down equal to fourth times the distance. In the direction. So work done is force times, distance moved in the direction of the force. So we have a water slide. The top of the slide is 32m above the bottom of the slide, so 32m. The total distance along the slide is 120. Nature, so 120. A person of 700 newtions, initially at rest at the top, slides down. His speed at the end of the slide is 15m per second. Calcullators, kinetic energy at the end of the slide. I and on end of the slide, end of the slide, okay, so 30, 120 total distance above the bottom of the bottom. Okay, so 700 mutants initially arrest sts at the top, slides down, hits speed at the end of the slide. And the end of the slide is 15m per second. So kinetic energy equal to the equal to a half and v squso. Knetic energy and and we know the we know the weight. So 700 divided by 9.81. And we also sorry, and we also know that the v square times 15 th. Times. Times 15 square square so and times no point five. And the end of 700 divided. About. Okay, kinetic energy you could do 8000 and tweight. Tschess. Yeah, that's what I get. Calculate the average resister force acting on him as he traels down to the end of the slide perstivity end of the slide. So first, the end of the slide, the resistiforce. A gravitational potential energy equal to mgh. So that is 32m and 700 divided by 9.81. And. H mg H, so mg is equal. So m times g is 700 newtons and times H 3:32, so 700 times 32, 2014 and -20 no. Let me see Yeah -2028 the 8028 so. Representational potential energy. So the. Energy. Resistive energy resist resistive energy equal to. And the average resistively. And we want to know about the. Energy equal to the. S so what all we know about is A S. I across syum. So I think 32 square plus 120 square and then square root. So we know the total distance along here is 120m, not a horizontal distance. So that is 120m. So if the whole distance is 120. 14, three, 72 divided by 120. 120 neuthus. Yeah the unit Smith. Pentilutions good. Okay, define work done by a force. Well, we've done that. So work is equal to force moved in the direction times the distance in the direction of the force. In the direction of the force. So that's where you get your second mowork to find power. Power power equto work down, divided by time, walk down per unit time. Explain why efficiency of a mechanical device can never be 100% mechanical device. Some manager there's. There some energy waste, for example, such as thermal energy. So energy will always get transferred to therminology in whole machines. I should say some energy will be transferred to thermal energy in all machines. The car has a total MaaS of 810 kilograms. Its speed changes from zero to 30m per second in 12s. Calculate the changing kinetic energy of the car. Changes from zero to 30m per second. That's underlying, right. It's. So kinetic energy note point five times 110 times 30 square. 3.7 times ten to the five. Calculate the average power generated by a car engine. Assume that the power generated by the engine is entirely used in increasing the kinetic energy of the car. 12s. 诶。I ate it by increasing energy. So if that is 3.7 times, ten to the five, so that is 12s. So this number. 3.7 times ten to the five divided by twelve. So the final answer is. 3.1 times ten to the four. Yeah. Read my turn to the floor. The efficiency of the car is 25%. The car takes 18 kilograms of petrol to fill its tank. The energy provided per kilogram of petrol is 46 megajoules per kilogram. The drag force acting on the car at a constant speed of 30 meper second is 500 newtions. Calculate the work done against the drag force per second. Some graphers. Against the drug force, against 30m walk down acting. So acting of the car at a constant speed of 30m is 500 newtons. Yeah that is my mark. So. Yeah work down equal to F S. Yeah that is worked down per second. So that's power 900 times. Yeah work done per second. So that is the power. Okay, 500 time times 30 equal to 1.5 times ten to the four. So. Work five. Work done is 500 times 30. So. Work done is 500. Times 30Yeah force times philosophy. So. 15000Yeah you got that. Calculate the total distance car can travel on a full tank of petrol and traveling at a constant speed of 30m per second. Yeah. No distance, total distance with the car can three measures ers per second distance. Full tank of petrol and they are constant speed. So we know the speed. We know the. Energy. We know it's 25%. Efficient air. No actual efficiency of the car are it's 25. So we can know that it's 25. So the the total energy of this tank this tank of petrol is is 46 times 18, equal to eight, 808, 828. M J mea juice per kilogram a if I times 8:18 kilograms, that is 828 megajles. So if the actual efficiency of the car is 25% divided by four, you 207. Maybe that's the answer. 200 no, 207 that is juice but the Jews but work down equal to fs. And that is the meter. So against the drag force, I suppose. So work done against the frictional force of drag force. So we have 207 megajles. Work available or energy storage. We know it's 500 newtons drag force times distance. So 207 million divided by 500. A million maker is a million. Oh, Yeah, lego. So two zero seven. The energy equal to the fs but where's the f? Sorry so that me is where's the 500? A drag force acting on the car at constant speed. So if you think of it, we have our car moving. In this direction. But there's a drag force acting on it, which is equal and oppoto the. So that's the drag force. And this is the thrust force. So I get 414 km, which sounds practical for a full tank of petrol. See, the clue is that it's moving at constant speed. If it only had one force acting on it, it would be accelerating all the time. But because it's moving at a constant speed, the this force is balanced by this force. So this is the drag force. The drag force, which is friction essentially. Okay. So they've done everything. Okay, write a word equation for kinetic energy. Fourth times distance. That's work done. Kinetic energy a half times MaaS, times velocity. Yeah a bullet of minus three by ten to the minus two kilogram is Farat a sheet of plastic or thickness. 1.5 cm, the bullet enters the plastic with a speed of 200m per second, and emerges from the other side with a speed of 50m per second. Calculate the loss of kinetic energy of the bullet as it passes through the plastic. So again, you have to do a half mv squared twice. Minus a half. 50 mesquage. So point five times three by ten to the minus two times 200 squared. So that's 600 joules initially. Minus. 50 squared times, three times to the minus, two times more five. 37.5 jouels. So the loss of kinetic energy. 562.5 so 562.5. The average frictional force exerted by the plastic on the bullet. So we know the thickness of the sheet of plastic. Okay, so 562.5. Is equal to the force the frictional force times the thickness of the sheet of plastic. It's going through point zero 15. Okay. So the force is that divided by that I get three, seven. Home five. Hilller newtons. Okay. So. I have some more exam style questions for us to try on Sunday. Jackson. So what what type of questions do you feel less comfortable with? Question maybe maybe the simple calculation maybe that I'm very confident for this. You are Yeah. What do you think you need more practice on? Well, as a logic answer, for example, do you explain how why like that? Yeah. Yeah so for example, a bouncing ball, why does the the puounheight decreases after each balance ounds air like that? Yeah. So you can see that the heist at the beginning, if it's dropped from 1m. It doesn't the height, the speed is less, so the kinetic energy is less, so the gravitational potential energy will be less, things like that. Okay, we'll just do the descriptive questions in this batch of questions next time. But you're getting there, Jackson. You're getting much more confident at working out what each question is looking for. Yeah. So keep at it. So we'll talk next on Sunday, we'll do a few more descriptive type questions and we'll discuss them. Okay, okay, I'll say goodnight then. Bye, bye. Bye, miss.