(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

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.

2. Relevant equations

Conservation of Momentum

Conservation of Energy

3. 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)

vf=13.716m/s

(.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)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Ballistic Pendulum Bullet

**Physics Forums | Science Articles, Homework Help, Discussion**