Why Isn’t Linear Momentum Conserved?

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

A thin metal bar, 2.00 m and a mass of 9.18 kg hangs vertically from a ceiling by a frictionless pivot. Suddenly it is struck 1.50 m below the ceiling by a small 3.00 kg ball, initially travelling horizontally at 10.0 m/s. The ball rebounds in the opposite direction with a speed of 6.00 m/s.

(a) Find the angular speed of the bar just after the collision. ***The answer in the textbook is 5.88 rad/s, and that makes sense to me.***

(b) During the collision, why is the angular momentum conserved but not the linear momentum?

2. Relevant equations

m*v(initial)*l = Iω + m*v(final)*l

3. The attempt at a solution

I have absolutely no idea how this is possible. I was always taught that momentum is always conserved.


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