(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A wooden block of mass M resting on a frictionless horizontal surface is attached to a rigid rod of length l and of negligible mass. The rod is pivoted at the other end. A bullet of mass m traveling parallel to the horizontal surface and perpendicular to the rod with speed v hits the block and becomes embedded in it.

What fraction of the original kinetic energy is list in the collision?

2. Relevant equations

KE = 1/2 m v^2

L = cross(r,p)

3. The attempt at a solution

The only way I can think of doing this problem is using linear momentum conservation.

Say if pi = m*v, pf = (m+M)v'

v' = v * m / (M+m)

final / initial Kinetic Energy = m / (M+m)

Unfortunately, the answer is M/(M+m).

I believe that I should be using conservation of angular momentum. According to part a of this problem (not stated) the angular momentum of the bullet+block = mvl.

If I were to use cons. of angular momentum, I don't really know to formulate it.

Initial Li = 0

Final Lf = mvl

Does anyone have any hints?

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# Homework Help: Bullet, Collision, Block

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