Hi, I'm Laura and today we're solving the problem 90 of chapter 3 open-stacks physics volume 3. This question involves kinematics and let's start. So here in the question we are giving an ambulance and a traffic light which is on Amber and an ambulance rushing a patient to the hospital with a speed of 72 kilometers per hour. We were asked that the time required is for the ambulance to reach the light before it turns red. That is in two seconds it is given the question. And a distance between the ambulance and the traffic light is 50 meters. So what should we do? If you want to do this question by yourself, you can stop the video now. I'll wait for a second. Okay, so here we should always start with writing the kinematics equations as you can see here. Then we should look at the units. What units will be required? We will be needing for this question. We are required in the option A we are asked the acceleration for the ambulance to have a rigid light in time. So we have 72 kilometers per hour and 50 meters. I assume that dealing with meters and seconds would be much easier. Here I convert the initial velocity to a different metric unit which is meters per second as you can see. And then we start calculating. Let's just say this point is our origin. So, writing the kinematics equation, this first equation, we have our light at 50 meters in the positive x direction. And equals x zero, our original destination is origin. So it's zero meters, I can write that. Plus, initial speed times t, which is 20 meters per second, as I calculated here, plus at times two seconds. Because we have to catch light in two seconds. Plus one halt, a two second squared. As you can see, through the calculations we get an acceleration of 5 meters per second in the positive x direction. And that is the end of this option A. In option B, the question asks that what is the final velocity of the ambulance when it catches the light? We can use these equations, the either one. But using this is much simpler because it's in a more confined form. So we have delta V which is equal to V minus V initial. What I denote with V here is the refining of the velocity. Minus our initial velocity is two and two meters per second. Equals 5 meters per second squared seconds because why? We have our acceleration which we have as 5 times delta t. The ambulance covers this distance in two seconds. So we have two seconds here. As you can see, the final velocity is 30 meters per second. But also you can use this equation which this is again the loss of final velocity. So we have V squared equals the initial velocity squared plus two times 5 because we have acceleration times 50 meters because the distance covered is 50 meters. So either way you end up with the final loss of 30 meters per second. Thank you for watching. Leave a comment if you made it.