Conservation of Momentum and Energy in Elastic Collisions

[mathewings]

A package of mass m is released from rest at a warehouse loading dock and slides down a 2.44 m high frictionless chute to a waiting truck. Unfortunately, the truck driver went on a break without having removed the previous package, of mass 7.00m, from the bottom of the chute. Suppose the packages stick together. What is their common speed after the collision?

Answer: 0.865 m/s

I solved this easily using kinematics to determine the small mass's velocity upon hitting the large mass. Then using conservation of momentum to isoalte the combined velocity. However, this secodn question confuses me:

Suppose the collision between the packages is elastic. To what height does the package of mass m rebound?

I've tried conservation of energy equations and always end up with a rebound to the original height of 2.44m. Can anyone offer suggestions?

 

[Hootenanny]

I've tried conservation of energy equations and always end up with a rebound to the original height of 2.44m. Can anyone offer suggestions?

What makes you think your answer is incorrect?

 

[Doc Al]

How did you set up your conservation of energy equation for the collision? (You still need conservation of momentum as well.)