posted by dave on .
at on time, the velocity of a rifle bullet was measured using a ballistic pendulum made up of a wooden block suspended from a string. the block used here has a mass of 20kg. a 50g rifle bullet is fired into the block, penetrating it by 10cm and causing it to swing upwards, increasing its height by 20cm.
a) calculate the velocity of the bullet as it enters the wooden block. Express you answer in km/h.
b) calculate the frictional force between the bullet and the wooden block.
Use conservation of energy (GPE=KEinitial) to find the velocity of the block/bullet at impact. Then, use conservation of momentum to find the initial velocity of the bullet at impact.
the work done by the bullet can be determined by energy:
KE of block/bullet-friction*.10m=KE bullet initial.