Question

A 3.0kg model train going right at 2.8m/s bumps into another 2.0kg model train in the same direction at 1.6m/s. The heavier train has a final speed of 2.2m/s to the right. What is the final speed of the lighter

2.0kg train car?

Answer 1

Momentum is conserved, so

(3.0 kg) (2.8 m/s) + (2.0 kg) (1.6 m/s) = (3.0 kg) (2.2 m/s) + (2.0 kg) v

where v is the final velocity of the lighter train.

Solve for v :

8.4 kg•m/s + 3.2 kg•m/s = 6.6 kg•m/s + (2.0 kg) v

5.0 kg•m/s = (2.0 kg) v

v = 2.5 m/s