Question

An empty 2,500 kg train car is headed northbound at a velocity of 5 m/s. Ahead of the first car, an empty 1,500 kg car is headed northbound on the same track at 1 m/s. The faster train bumps into the slower one, and they combine into one train. What is the velocity of the two-car train?

Answer 1

C: 3.5 m/s

Step-by-step explanation:

Answer 2

Let the mass of 2500 kg car be
`m_1` and it's velocity be
`v_1` and the mass of 1500 kg car be
`m_2` and it's velocity be
`v_2` .

After the bumping the mass be M and it's velocity be V.

By law of conservation of momentum we have

`m_1v_1+m_2v_2 = MV`

2500 * 5 + 1500 * 1=4000 * V

V = 14000/4000 = 7/2 = 3.5 m/s

So the velocity of the two-car train = 3.5 m/s