A big toy school bus rear-ends a small toy school bus initially at rest. The bigger bus is several times heavier than the smaller one. Which of the following statements are true if the collision is totally inelastic?

1. The big bus exerts the same amount of force on the small bus as vice versa.

2. The two buses continue together at the same speed.

3. Mechanical energy is conserved.

4. Momentum is conserved.

5. The big bus will go backwards.

I put:

1. True
2. False
3. False
4. True
5. False

...but apparently one or more of the answers is incorrect. Please help?