Conservation of Angular Momentum Conceptual Question

3. A metal bar is hanging from a hook in the ceiling
when it is suddenly struck by a ball that is moving
horizontally (see figure). The ball is covered with
glue, so it sticks to the bar. The collision takes place
over a very short time span. During this collision
a) the angular momentum of the system (ball and bar) is conserved about the hook because only gravity is acting on the system.
b) the angular momentum of the system (ball and bar) is not conserved because the hook exerts a force on the bar.
c) the angular momentum of the system (ball and bar) is conserved about the hook because neither the hook nor gravity exerts any torque on this system about the hook.
d) both the angular momentum of the system (ball and bar) and its kinetic energy are conserved.
e) both the linear momentum and the angular momentum of the system (ball and bar) are conserved.
4.

I know the answer is c, but I don’t know why linear momentum is not conserved….

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