 So in this question, it's given that two cars A and B are moving along in a straight line. Car A is moving at a speed of 80 kilometers per hour and car B is moving at a speed of 50 kilometers per hour in the same direction. Find the magnitude, so one, in direction of the relative velocity of car A with respect to B. Okay, so and the relative velocity of car B with respect to A. So what is relative velocity? So our first task draw a diagram. Let's say this is car A. Okay A and this one is car B. Okay, now what is happening? Two cars A and B are moving along a straight line. That's done. Car A is moving at a speed of 80 kilometers. So let's say V and I am writing A subscript A, V A in this direction. And V A I know is V A is 80 kilometers per hour, 80 kilometers per hour and V B is 50 kilometers per hour. Now it's not mentioned whether A is initially moving towards B or B is moving towards A. So let us assume this is a case. Okay, this is VB. Fantastic. Now what? It's only given that cars A and B are moving along in a straight line. Car A is moving at a speed of 80 kilometers per hour while car B is moving at a speed of 50 kilometers per hour in the same direction. Find the magnitude in direction of relative velocity of car A. So relative velocity of car A with respect to B is written like this. V A B. So relative velocity of, this is I'm saying relative, relative velocity of A with respect to B. Correct? So V A B is given by V A minus V B. V A minus V B. Okay, so whatever is the velocity of A minus whatever is the velocity of B. And if you see what is velocity of A, 80 kilometers per hour towards right and B is 50 kilometers. So hence minus 50 kilometers per hour. I'll have to take, you know, both V A and V B are in the same direction. So simply minus. Let's say they were in opposite direction. Then I would have done V A minus, minus V B. Understood? Right now V A and V B in this case are in the same direction. So hence this is 80 and this is 50. So difference is 80 minus 50. Let us say V A would have been, so it's better to also see cases like this, like that. Okay, so V A towards right, V B is right. So let's say if you take towards right as positive, then automatically this will become minus 50. So hence relative velocity would have been V A minus V B, 80 minus minus 50. Okay, so that will be nothing but 130. Right, in this case 30. So you've got the difference. So if the velocities are in the same direction, so simply subtract the magnitude. So what is the value guys? 30 kilometers per hour. Now what does it mean? Let's say if V A and V B are same. V A is equal to V B. Let's take that case. In an airplane, you are moving. So your co-passengers are having same velocity like you and that is equal to the airplane's velocity. Now you and your co-passenger appear to be rest with respect to each other. But someone who is in the ground or someone who is on another plane or moon or sun, wherever, he will see that both of you are moving together with the same velocity. So that's what is the relative velocity understood. So inside the plane, the co-passenger is appearing to be at rest with you with respect to you. Correct? Why? Because both of your velocity are same and in the same direction. So hence V A minus V B becomes zero. Okay, so they appear to be at rest with you. But let's say if in the same plane one, you know, you just get up and start moving towards the pilot's cabin, let's say you start moving, then let's say you are A, you are person A. And V B is your co-passenger sitting at the same spot. Then he will see that you are moving away from him, isn't it? Though he's also moving, let's say at a speed of 800 kilometers per hour, which is the speed of the plane. And you also are moving with 800 kilometers per hour when you are sitting on the, on your seat. And then you get up and you started moving towards pilot's cabin with let's say five or one meter per second speed, something like that. Or in the same units we'll have to take, but let's say something. So what will happen? The you will appear to be moving with one meter per second with respect to B. So V B, the person B will see that you are moving away from him at one meter per second speed only, isn't it? Same is the case here guys, right? So hence now someone who's, you know, at the relative velocity of car with respect to B, right? So the B person B or the car B would find what that you are, the A is coming towards you with this speed. Okay? So he will feel that V A or the car A is coming towards car B with this much speed, right? Towards B, correct? Now what is the other way around? V B A, what would a passenger in car A feel about B? Okay? So V B A is simply, you know that V B minus B A. Now what is V B? 30 kilometers per hour. Okay? 30 kilometers per hour. And what is V A is 50 kilometers per hour. Sorry, sorry my bad. It's not 30. It is, it is 50. This one, sorry, let me cut it or let me just undo it. Okay? So V B. So what is V B guys? V B is 50 kmph and minus 80 kmph, correct? It comes out to be minus 30 kmph. What does this mean? Right? So V B or V A will see that V B is moving minus 30 kmph away from him. That means this is 30 kmph towards A. Right? So hence, passenger of A would see B to be coming towards A. Let me use this color. And so hence this is V B A. Okay? So if you are in passenger A's position, car A position, so the car B would be appearing to be coming towards you. Isn't it? With time and eventually you guys will collide. Okay? Because you have a, because A has a higher speed and the passenger B here will see V A to be coming with this velocity towards B, 30 kilometers per hour. Isn't it? So this is what is the concept of relative velocity. So always remember, velocity of A with respect to B is V A minus V B. Okay? And velocity of B with respect to A is V B minus V A like that. So I hope you understood this problem. Now let's go to second problem.