Solving a Momentum Problem: Bullet-Block System with Spring Compression

[mohamud3917]

A 11.0-g bullet is fired horizontally into a 108 g wooden block that is initially at rest on a frictionless horizontal surface and connected to a spring of constant 154 N/m. If the bullet-block system compresses the spring by a maximum of 76.0 cm, what was the velocity of the bullet at impact with the block.

what i did first was i set F=kx to find the force the bullet block system applied to the spring.

after solving for F, i couldn't find a way to relate force to the momentum equation
m₁v_1i=(m₁+m₂)v_f

 

[Doc Al]

what i did first was i set F=kx to find the force the bullet block system applied to the spring.

Instead of worrying about the force, consider the energy stored in the spring.

 

[mohamud3917]

ok so how do i set it up

 

[Doc Al]

Think of the problem as having two parts:
(1) The collision itself. What's conserved during the collision?
(2) The compression of the spring after the collision. What's conserved here?