1. The problem statement, all variables and given/known data A bullet of mass m and speed v passes completely through a pendulum bob of mass M. The bullet emerges with a speed of v/2. The pendulum bob is suspended by a stiff rod of length L and negligible mass. What is the minimum value of v such that the pendulum bob will barely swing through a complete vertical circle. Basically, what occurs is a bullet m is shot through a mass M which is suspended by a rod and pinned on the wall (it pivots in a circle). The problem asks for the minimum value of v so that M will spin in a circle once if the bullet emerges with a speed of v/2. 2. Relevant equations m1v1+m2v2=m1v1'+m2v2' Maybe a work/energy equation? 3. The attempt at a solution I understand that the momentum of the bullet is transferred to the pendulum which is why the pendulum swings around and the bullet leaves with half the velocity it entered with, but I don't know how to find the amount of energy it takes to spin the pendulum. Any help would be greatly appreciated.