7. What is the force on a 1000 kg elevator that is falling freely under the acceleration of gravity only (10m/s?)?

The answer is 1000x10= 10000N

The force should be its weight. This is the force (gravitational) between the Earth and the elevator...the only thing is that the Earth is too massive to "see" the effect of this force (movement) while you see the elevator speeding towards the Earth (with acceleration
g
).
So:

An elastic collision is a collision in which there is no net loss in kinetic energy in the system as a result of the collision. Both momentum and kinetic energy are conserved quantities in elastic collisions!