A 10,000 kg railroad car traveling north at 10 m/s collides with a 5,000 kg rail car also moving north but at an unknown speed. After the collision, the two cars lock together and move north at 8 m/s. How fast was the second car moving before the impact?

Answer 1

Given:
M1 = 10,000 kg, V1 = 10 m/s.
M2 = 5,000 kg, V2 = ?
V3 = 8 m/s = Velocity of M1 and M2 after colliding.

Momentum before = Momentum after.
M1*V1 + M2*V2 = M1*V3 + M2*V3.
10,000*10 + 5000*V2 = 10,000*8 + 5000*8,
V2 = ?

Answer 2

0.875