posted by RD .
A bullet of mass 3.2 g strikes a ballistic pendulum of mass 3.6 kg. The center of mass of the pendulum rises a vertical distance of 13 cm. Assuming that the bullet remains embedded in the pendulum, calculate the bullet's initial speed.
you can only use conservation of momentum on the collision
Now you can consider energy after the collision
in the second equation, solve for Vf, then put it in the first equation, and solve for Vi.