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**[SOLVED] Conservation of momentum + elastic collision**

Hey guys, I couldn't even start this one, tried to think about it, but I'm hitting a blank

A block of mass m = 2.20 [kg] slides down a 30 degrees incline which is 3.60 [m] high. At the bottom, it strikes a block of mass M = 7.00 [kg] which is at rest on a horizontal surface. (Assume a smooth transition at the bottom of the incline.) If the collision is elastic, and friction can be ignored, determine A) the speeds of the two blocks after the collision and B) how far back up the incline the smaller mass will go.

know: m = 2.20kg

theta = 30 degrees

h = 3.60m

M = 7.00 kg

Ok so I don't understand how to find the velocity when the blocks start. I know that the collision in elastic so momentum is conserved, but should I use conservation of energy or dynamics to solve for it?

Any help would be great. Thank you!