# Homework Help: Bullet in block

1. Oct 23, 2005

### Punchlinegirl

A bullet of mass m= 0.0260 kg is fired along an incline and imbeds itself quickly into a block of wood of mass M= 1.30 kg. The block and bullet then slide up the incline, assumed frictionless, and rise a height H= 1.20 m before stopping. Calculate the speed of the bullet just before it hits the wood. Note. The block is kept from sliding down the incline initially by as small peg (not shown).
I know that I need to use conservation of momentum, but I'm not sure how I would do that since I don't know the final velocity. I don't even know how to find it since I don't know the angle of the incline of the length of the incline.
Thanks

2. Oct 23, 2005

### Päällikkö

What is the velocity required for the block (with the embedded bullet) to reach a height of 1,20 m?

3. Oct 23, 2005

### Fermat

Start by thinking about conservation of energy.
What kind of eqn(s) are/is involved in doing that ?

4. Oct 23, 2005

### Punchlinegirl

Ok for conservation of energy
I used (1/2)mv_initial^2=Mgh
(1/2)(.0260)v^2= (.0260+1.30)(9.8)(1.20)
Solving for v gave me 34.6 m/s.
Am I doing that right?

5. Oct 23, 2005

### Päällikkö

No, you are not. You cannot assume energy conservation during impact (unless it is stated that the collision is elastic, which is not the case in this problem).

After impact, however, energy is conserved.

6. Oct 24, 2005

### Punchlinegirl

I figured out what I was doing wrong. Thank you.