Short revision for Work Energy Power in 12 minutes!Must watch before you exams

Added: 2026-05-12

[00:00:00]Guys, since a lot of you guys are rushing for your exams tomorrow, I know uh you have to cover a lot of topics, but this one chapter, work, energy, power, is a topic that a lot of you guys can't really comprehend in just one day.

[00:00:16]So, I'm going to be trying to speedrun all of these and I hope you get the gist of it. So, what is work actually? So, what work actually is? is basically the product of force into distance.

[00:00:30]Basically, think of uh pulling an object in front of you. You're giving it a force and it traveled a distance. And the work is basically the force you gave into the distance it traveled. So basically think about it in this way. If let's say you pulled an object in a different angle, right? With respect to that angle, I can say that the work is equals to F cos theta. Theta is basically let's say you pulled an object like this. Theta is basically this angle into the distance traveled. Okay. The distance is denoted by S or X. It's your wish. Okay. So we need to understand two types of energy. Okay. So elastical potential energy is not in your syllabus. It's in further maths. So all you have to learn is gravitational potential energy GPE and kinetic energy.

[00:01:24]Okay. So kinetic energy is basically the energy of anything that is moving with a velocity V. Okay, let's say you're running, you are gaining kinetic energy.

[00:01:37]Okay, and GP is basically the pull of gravity, right? So basically, let's say you go up, you go up, your GPE increases. Okay? And you go down, you're going with the gravity, right? your GPE actually decreases because of that reason. Okay, you have to remember that when you go up your GP increases because you're going against the gravity and when you go down you're going with the gravity so it decreases. Okay. Okay. For kinetic energy if your speed increases your K increases. If your speed decreases your K decreases. Okay. And what and you have probably learned this in your O levels physics. So I'm not going to go in depth about it. But what's new in eight levels uh mechanics is that the formula has been changed to mg of change in height and half mv of change in speed. Okay. All right. Now for power. Power is basically rate of change of work done. Okay. So if I take this work done, I can also write this as F into distance over this. Right? I can also write this like this, right? And we know that distance over time is basically equals to velocity. So I can also write the formula as FV. But you do have to make sure that this formula is only applicable for the driving force.

[00:03:07]Okay? By driving force, I mean the force you are giving to an object to make it go forward. Okay, not the one where you project it. Okay, so the unit of this is for is what? This is not really important. Okay, so for smooth surface, let's say a surface is smooth. Let's say this is a ball. If it goes up, its P increases. Okay, but as it's going up, its K actually decreases. Okay.

[00:03:38]And let's say for an object if it goes down its PE decreases but its K actually increases.

[00:03:46]Think of it like a real life scenario.

[00:03:48]Okay? You're running up. The gravity is working against you. So your speed is basically decreasing. Okay? And you're going down.

[00:03:59]You're going down.

[00:04:02]You're working with the gravity. So your PE decreases but your velocity increases. Okay. So this is the most important formula in all of this chapter. What you have to remember is that the work inputed plus the initial kinetic energy and the initial GPE is equals to the work outputed plus the final kinetic energy and the final GPE.

[00:04:28]So I took some questions from Penguin's past paper which must help you uh get the concepts correct. Okay. So here a particle is dropped. Dropped means that I'm not giving it any external force from a height of 9 m above the horizontal ground. If we think of it like a diagram, a particle is dropped from 9 m. Okay. The speed of the particle at instant before it hits the ground is 12 m/s. So when it hits the ground, its velocity is 12 m/s.

[00:05:06]Okay. Find the work done against the air resistance. The air particles that's giving it a force. We have to find the work done due to it. Okay. So we can see that the work inputed is basically nothing. Okay. I just dropped it. Okay.

[00:05:21]And the kinetic energy initially is just zero because the speed is zero. Right?

[00:05:30]>> Okay. So what they did is they took it took this as the base level but I wouldn't actually recommend you to do that. What I would do is please give me a minute.

[00:05:47]Um, [snorts] okay.

[00:06:02]What I would do here is the kinetic energy is obviously zero. I'm going to take this GPE as uh 1.6 6 into 10 into 9. All right. And then I'm going to take the final kinetic energy as this.

[00:06:24]And what I'm going to do is I'm going to take the final GPE to be zero because this is the baseline, right? And we have to find the work out. Okay, you can see this is basically the same calculation and this gave me an answer of 28.8. All right, so for the next question, a block of mass 4 kg is pushed up a line of greater. Okay, so for this questions, I highly recommend you to draw a diagram.

[00:06:59]So this is inclined at 30° and this is actually pushed up. The particle is actually pushed up. All right.

[00:07:09]The direction of B.

[00:07:13]Okay.

[00:07:15]The particle passes through point Q, P and Q with speed this and this respectively. Let's say point P is here.

[00:07:27]Oh, I'm so sorry.

[00:07:37]>> Let's say point P is here. The velocity of this is 12, right?

[00:07:51]And let's say point Q is here and the velocity of this is just eight. Find the decrease in kinetic energy of plug at is at as it moves from P to Q. So what we have to do is we have to find the change in kinetic energy. Okay. So what he did is he f found the initial kinetic energy in P and he found the final kinetic energy in Q. You see that it actually decreased. So we can say that the change in K is 160 Jew which decreases. Okay, that was pretty simple. And for the next part, he wants me to find the work done by the force pushing. Okay. So basically he wants me to find the work I have inputed for it to reach Q. Right?

[00:08:40]Okay. So we have to find the W. We know the initial kinetic energy already. We know the final kinetic energy already here. Okay. So for the final P I take I took this as the baseline.

[00:08:55]So P here is just zero. So I have to find the P here. Right. So I need the height for it. So how can I find the height?

[00:09:08]I can just take this as 30°.

[00:09:12]I have to find the height. So let's just make a triangle.

[00:09:18]This is 30. This is 90. This is my height. And this is just 10 m apart.

[00:09:23]Right?

[00:09:25]So I can find the height as 10 sin theta.

[00:09:31]See he did the same thing right and the work out is zero. Why? Because it's a smooth plane and after all those work you find the work done to be 40 jewel.

[00:09:43]Okay.

[00:09:44]Okay. Now for the final type of math.

[00:09:47][snorts] A car of mass this is traveling along a straight horizontal road with its engine working at a constant rate of power. The resistance to the motion of the car is equals to r newton. When the speed of the car is 19 m/s, the acceleration is this. When the speed of the car is this, the acceleration is this. All right, we have to find a value of P and R. Here the P is actually the work and the R is actually the resistance. Okay, so we all know that F minus R is just equals to MA. This is the Newton second law.

[00:10:28]So we also know that the formula of power is f into v. So we can just write that f is equals to p / v. So this is exactly what I have done here. So what I have done is I have arranged a formula just like this and I have just put the values here.

[00:10:51]Okay. See for v = to 19 I have taken acceleration of 0.6 okay and for v = to 30 I have taken the acceleration of 0.16.

[00:11:07]So after that I have found two equations which I will just simultaneous and find the value of p and r and that should be work energy power. I know I have been rushing a lot, but I hope this chapter will be done for you and you're going to be able to score tomorrow.