Question

You find yourself standing in front of a run-away train armed with an unlimited number of baseballs. The only way to stop the train is to throw the baseballs at the train, and have the train conductor catch them (i.e., it is an perfectly inelastic collision). Assume the train is moving at 45 kph (10 m/s), and that you can throw a baseball at 110 mph (50 m/s). The train has a mass of 100000 kg. Take the mass of the baseballs to be 100 g (0.1 kg). How many baseballs do you need to throw at the train to stop it?

Answer 1

Here we have given that,

Speed of train = 10 m/s

Speed of a single baseball = 50 m/s

Mass of train = 100000 kg

Mass of a baseball = 0.1 kg

Now using the condition of inelastic collision here we have to keep the final velocity of the combined system of train and baseball to be zero so that, let n numbers of base ball is required to stop the train so that,

nMbVb - MtVt= (Mb+Mt) × Vf

Here Vf = 0

So that,

n = MtVt/MbVb = 100000×10/0.1×50 = 200000

Hence the number of baseball requirements here will be to stop the train is 200000