A 7.0-g bullet is fired into a 1.5-kg ballistic pendulum. The bullet emerges from the block with a speed of 200 m/s, and the block rises to a maximum height of 12 cm. Find the initial speed of the bullet.
Now I think this is an imperfect inelastic collision because the bullet does not lodge itself in the pendulum. So I assumed since it was inelastic I could ignore conservation of kinetic Energy.
Conservation of Momentum
Conservation of Energy
The Attempt at a Solution
m1v1i +m2v2i=(m1 + m2)vf
(.007kg x v1i)+0=(1.507kg)vf
(PE + KE)collision=(PE + KE)top
0 + (.5 x 1.507 x vf^2)= mgh + .5mv^2
0 + (.5 x 1.507kg x vf^2) = (1.5 kg x 9.81m/s^2 x .12m) + (.5 x .007kg x 200^2)
vf^2=(1.7658J + 140J)/(.7535kg)
(.007kg x v1i)=1.507kg x 13.716m/s
v1i = 2952 m/s
Now I know this is not the answer because the answer is given as 530m/s but I can't for the life of me figure out what went wrong with the energy calculation. (I'm assuming that's where the big boo boo happened)