# Bullet Momentum problem

1. Jul 6, 2009

### balling12

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 12.6 cm. Find the initial speed of the bullet.

2. Relevant equations

3. The attempt at a solution
I used the equation:
(Mbullet)(Initial Velocity)+(Mpend)(Initial Velocity)=(Mb)(Fvelocity)+(Mp)(Fvelocity)
Once i plugged in all of the information i have i came to the answer of 306.5 but it is incorrect.

2. Jul 6, 2009

### Staff: Mentor

Conservation of momentum applies to the collision of bullet and block, but how did you make use of the maximum height? (You'll need a second equation.)

3. Jul 6, 2009

### balling12

For my second equation i used (.5mvf^2)-(.5mvi^2)= -(mgyf-mgyi)
when i solved: vf=.49

4. Jul 6, 2009

### Staff: Mentor

Show exactly how you got that result.

5. Jul 6, 2009

### balling12

Initial V Of Pend= 0 Initial Height of Pend= 0
so (.5)mvf^2= -mgyf
masses cancel
vf= square root[ (2)(g)(0.0126)]
=.49

6. Jul 6, 2009

### Staff: Mentor

12.6 cm = 0.126 m (not 0.0126).

7. Jul 6, 2009

### balling12

dang that was my problem lol. thanks