How Do You Calculate the Mass of a Block from a Bullet and Spring Collision?

[blindsided]

Homework Statement

A 34g bullet traveling 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.

Homework Equations

Not sure.
m₁v₁ + m₂v₂ = (m₁ + m₂)v'
E_e = .5kx²
E_k = .5mv²

The Attempt at a Solution

I'm fairly certain it's incorrect. I just don't know where.

Thanks!

 

[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 system would have to be very small meaning a very large mass for the block.