Question

A 5000 kg train is traveling at a velocity of 100 m/s and hits another train. The two trains stick together and the new velocity is 50m/s. What is the mass of the second train?

Answer 1

Answer:

Explanation:

Conservation of momentum is used to solve

Unfortunately we have a missing piece of information such as the initial velocity of the unknown mass train.

If we ASSUME that the second train is at rest

5000(100) + m(0) = 5000(50) + m(50)

which means m = 5000 kg

However, I'll show you the importance of knowing that initial velocity by finding it assuming the other answers are valid

if m = 15000 kg

5000(100) + 15000(v₀) = (5000 + 15000)(50)

v₀ = 33 ⅓ m/s

if m = 10000 kg

5000(100) + 10000(v₀) = (5000 + 10000)(50)

v₀ = 25 m/s

if m = 8000 kg

5000(100) + 8000(v₀) = (5000 + 8000)(50)

v₀ = 18.75 m/s

So you can see why I had to assume an initial velocity. Any of the masses could work if the initial velocity is chosen correctly.