Question

A bullet of mass m is fired with a speed v at a wooden block of mass M which is hanging from the ceiling. The block swings upward and reaches a maximum height of h. By measuring h, we can find the initial speed of the bullet v.

a.) Let's say at time t = t₀ the bullet has not yet hit the block. At time t=t₁ the bullet/block system is lodged in the block and the bullet/block system is now moving with a new velocity v', but has not yet changed height significantly. Is momentum conserved between t₀ and t₁? Is energy? Explain why or why not.

b.) Now at time t = t₂ the bullet/block system has reached its maximum height h. Is momentum conserved between t₁ and t₂? Is energy? Explain why or why not.

M+m m

Answer 1

In both parts (a) and (b) , the moment is conserved whereas in both parts (a) and (b) , energy is not conserved. It is so because, the collision is an inelastic collision and we know that moment remains conserved in inelastic collision whereas energy doesn't remain conserved in inelastic collision.