# Homework Help: To what depth will the bullet penetrate the block in this case?

1. Nov 30, 2008

### frosti

1. The problem statement, all variables and given/known data
A 7.00 g bullet, when fired from a gun into a 1.00 kg block of wood held in a vise, penetrates the block to a depth of 7.60 cm. This block of wood is next placed on a frictionless horizontal surface, and a second 7.00 g bullet is fired from the gun into the block. To what depth will the bullet penetrate the block in this case?

2. Relevant equations
m1v1 + m2v2 = (m1+m2)vf

3. The attempt at a solution
I have no clue how to solve this problem. I don't really know what to do with the depth of penetration by the bullet. Can anyone please help?

2. Dec 1, 2008

### PhanthomJay

Re: collision

There's a significant loss of KE in part 1....like all of it, 1/2mv_b^2. In part 2 , apply conservation of momentum, and determine the total loss of KE. It' ll be a bit less; how does that ratio difference relate to the new depth of penetration?