You are driving along the road in a rented movingvan. It\'s full of all of your

Question

You are driving along the road in a rented movingvan. It's full of all of your possessions, so you and the loadedtruck weigh 4000 kg. You have just slowed down to 7 m/s (about 15mph) because you're in a school zone. It's a good thing you thoughtto do that because a group of first graders are just starting tocross the road. Just as you pass the children you see a 1000 kgsports car in the oncoming lane heading straight for the childrenat 40 m/s (about 90 mph). Oh no! A desperate thought crosses yourmind: you have just enough time to swing into the oncoming lane andspeed up a bit before making a head-on collision with the sportscar! Assuming that the collision is inelastic, how fast doyou need to go to stop the sports car? Can you save thechildren?

Explanation / Answer

If the collision is inelastic, the final speeds of both the vehicles would be same, ie.zero. So, by conservation of linear momentum, M1v1 + M2v2 = 0 So, v1 = -M2v2/M1 = -1000*40/4000 = -10 m/s ie. 10m/s in the direction opposite to the sports car. Since you are slower than that, ie. 7 m/s, you cannot save the children unless you accelerate toatleast 10 m/s.

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