Question

A bullet of mass m strikes a block of mass M. The bullet remains embedded in the block.

Answer 1

You have to use Conservation of Momentum here,

Let ,

mv = (m+M) V

where V is a velocity of block and bullet combined after hit.

Now, when Block rises up the kinetic energy of block converted into potential energy.

so,

1/2 (m+M) V^2 = (m+M)gh

V^2 = 2gh

V = √2gh

so, we get

v = ( (m+M) ×√2gh) / m