Question

Train car A is at rest when it is hit by train car B. The two cars, which have the same mass, stick together and move off after the collision. How does the final velocity of train cars A and B after the collision compare to the initial velocity of train car B before the collision?

The final velocity is double train car B’s initial velocity.
The final velocity is the same as train car B’s initial velocity.
The final velocity is half of train car B’s initial velocity.
The final velocity is zero, since train car B will stop.

Answer 1

The final velocity is half of train car B’s initial velocity.

Explanation: Momentum is conserved: m v_B = (m + m) v_final → v_final = (m v_B)/(2m) = v_B/2. (Kinetic energy is not conserved in this inelastic collision.)