Elastic Collision / Energy Preserved

Homework Statement

A block of mass m1= 5kg is released from point 1 which is 5 meters above the horizontal frictionless surface and slides down a frictionless track. It makes a head-on collision at point 2 with a block of mass m2= 10kg that is initially at rest. Calculate the maximum height to which m1 rises after the collision.

I don't know where to start... The problem doesn't give the distance between m1 and m2, just how far m1 is above the ground.

The Attempt at a Solution

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Use energy conservation + conservation of momentum. You know that since the sliding block isn't losing energy to friction, that all it's energy must be in the form of kinetic and potential energy. At the point it's released, all of it's energy is in the form of gravitational potential energy. By the time it hits block 2, all of it's energy must be kinetic, so you'll be able to figure out the velocity of impact. Now, you combine what you know about energy-momentum conservation with the fact that block 1 is going to bounce a little back up the ramp, meaning you'll still have to look at gravitational potential energy and that should do it.