A 15 g bullet strikes and embeds in a 2.8 kg block suspended at the end of a 1 m string. After the collision the string rises to a maximum angle of 20 degrees to the vertical.

Question

A 15 g bullet strikes and embeds in a 2.8 kg block suspended at the end of a 1 m string. After the collision the string rises to a maximum angle of 20  degrees to the vertical.
what is the speed of bullet?

bobpursley · Answer

figure how high the blocks/bullet went.
then figure potential energy (mgh) it increased. That is equal to the initial KE of the block/bullet

figure the velocity of the block/bullet from the KE.

Now,having the initial veloctiy block/bullet,you can find the initial momentum of the bullet from conservation of momentum,thence its velocity.