A block of mass 2 kg travels along a horizontal frictionless surface
with velocity 3 m/s. The mass collides with another mass, m, and
rebounds with velocity 1 m/s. Mass m is initially at rest. What is the
kinetic energy of mass m after the collision?

1. 10 J
2. 6 J
3. 2 J
4. -4 J
5. -8 J
6. None of the above.
7. Not enough information.