A 1.6-kg block is attached to the end of a 2.0-m string to form a pendulum. The pendulum is released from rest when the string is horizontal. At the lowest point of its swing when it is moving horizontally, the block is hit by a 10-g bullet moving horizontally in the opposite direction. The bullet remains in the block and causes the block to come to rest at the low point of its swing. What was the magnitude of the bullet's velocity just before hitting the block?

Question

~a friend · Accepted Answer

The kinetic energy = the original potential energy, so KE = mgh = .5mv^2

Solve for velocity to get 6.26 m/s for the block

Since Vf = 0, use inelastic equation to get m2v2=-m1v1 and solve for v2
v2 = 1540 m/s