Question

On a frictionless horizontal air table, puck A (mass 0.246 kg) is moving to the right toward puck B (mass 0.667 kg), which is initially at rest. Puck A collides inelastically with puck B. After the collision, puck A has velocity 0.207 m/s to the left, and puck B has velocity 0.532 m/s to the right.

1. What was the speed of puck A before the collision?
2. Calculate the initial kinetic energy of puck A.
3. Calculate the change in total kinetic energy of the system that occurs during the collision.

Answer 1

1) Use momentum conservation:

$$mv=-mv_m+Mv_M,\\ v=1.235\text{ m/s}.$$

2) The initial energy:

$$Ke=0.5mv^2=0.188\text{ J}.$$

3) The change is the difference between the initial energy and final energies of both pucks:

$$∆=Ke-Ke_m-Ke_M=0.0883\text{ J}.$$