A ballistic pendulum is a device for measuring bullet speeds. One of the simples

Question

A ballistic pendulum is a device for measuring bullet speeds. One of the simplest versions consists of a block of wood hanging from two long cords. (Two cords are used so that the bottom face of the block remains parallel to the floor as the block swings upward.)

1. A 0.013-kg bullet traveling at 280 m/s hits a 2.0-kg ballistic pendulum. However, the block is not thick enough for this bullet, and the bullet passes through the block, exiting with one-third of its original speed. How high above its original position does the block rise?

Explanation / Answer

from the conservation of momentum

m1u1+m2u2 = m1v1+m2v2

0.013*280+2*0 = 0.013*280/3+2*v

v = 1.213 m/s

from the conservation of energy

mgh = 1/2mv^2

h = v^2/2g

h = 1.213^2/2*9.8

h = 0.075 m

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