A ballistic pendulum, as shown in the figure, was a device used in the past century to measure the speed of bullets. The pendulum consists of a large block of wood suspended from long wires. Initially, the pendulum is at rest. The bullet strikes the block horizontally and remains stuck in it. The impact of the bullet puts the block in motion, causing it to swing upward to a height . If the bullet has a mass of 8.3 g, and the block of mass 6.6 kg swings up to a height of = 7.000 cm, what was the speed of the bullet before impact?

Question

A ballistic pendulum, as shown in the figure, was a device used in the past century to measure the speed of bullets. The pendulum consists of a large block of wood suspended from long wires. Initially, the pendulum is at rest. The bullet strikes the block horizontally and remains stuck in it. The impact of the bullet puts the block in motion, causing it to swing upward to a height . If the bullet has a mass of 8.3 g, and the block of mass 6.6 kg swings up to a height of  = 7.000 cm, what was the speed of the bullet before impact?

bobpursley · Answer

The momentum of the bullet equals the momentum of the block/bullet after impact. the energy of the block/bullet converts to potential energy in rising to the height.

So work backwards, and solve for velocity of the bullet.