A ball is attached to one end of a wire, the other end being fastened to the cei

Question

A ball is attached to one end of a wire, the other end being fastened to the ceiling. The wire is held horizontal, and the ball is released from rest (see the drawing). It swings downward and strikes a block initially at rest on a horizontal frictionless surface. Air resistance is negligible, and the collision is elastic. The masses of the ball and block are, respectively, 1.8 kg and 2.5 kg, and the length of the wire is 1.21 m. Find the velocity (magnitude and direction) of the ball (a) just before the collision, and (b) just after the collision. I found a, but not b... Please explain how to get KEafter/KEbefore

Explanation / Answer

Energies must be used for this, Energy = mgh = 1/2mv^2, with this you can derive a function of speed upon collision, which is Square root(2gh). You get this from rearranging and factoring out the mass. (btw....h=L).

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