# Accounting for momentum in a collision

**1. The problem statement, all variables and given/known data**

Consider a bar of length L, mass M, and uniform density floating in free space (ie: neglect gravity and assume that it is not contacting anything). The bar is initially stationary. Imagine a bullet of mass m travelling at a speed v hits the bar at one end. What is the linear momentum of the bar, the angular momentum of the bar, and the linear momentum of the bullet after the collision?

**2. Relevant equations**

p_bullet = mv before collision

Momenta of the bar are zero, for both angular and linear.

**3. The attempt at a solution**

The best I can come up with is that in the collision, we have:

mv = p_bar + Jw_bar + mv2

Where v2 is the speed of the bullet after collision and Jw_bar is the angular momentum of the bar. The problem I’m having is I can’t figure out how to find the expressions for p_bar and Jw_bar in terms of the known variables M, m, and v.

http://ift.tt/1err6Dy

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