# Homework Help: Energy? Momentum? Collision?

1. Jan 25, 2009

### blindsided

1. The problem statement, all variables and given/known data
A 34g bullet travelling at 120m/s embeds itself in a wooden block on a smooth surface. The block then slides toward a spring and collides with it. The block compresses the spring (k=99N/m) a maximum of 1.2 cm. Calculate the mass of the block of wood.

2. Relevant equations
Not sure.
m1v1 + m2v2 = (m1 + m2)v'
Ee = .5kx2
Ek = .5mv2

3. The attempt at a solution
I'm fairly certain it's incorrect. I just don't know where.

Thanks!

2. Jan 25, 2009

### chrisk

I see your concern with the mass of the wooden block. Your approach is correct. Consider the spring. It has a spring constant of 99N/m. This means if the spring were used as a scale a 10 kg mass would compress the spring 1 meter. A very weak spring. Since the spring compressed .012 meters your answer is reasonable; the velocity of the bullet-block sytem would have to be very small meaning a very large mass for the block.