Simple harmonic motion and amplitude

[Dotty21690]

Homework Statement

A 2.10-kg block is suspended from a spring with a spring constant of 280.0 N/m. A 0.070-kg bullet is fired into the block from directly below with a speed of 220.0 m/s and is embedded in the block. Find the amplitude of the subsequent motion.

-What fraction of the original kinetic energy of the bullet appears as mechanical energy in the system of block-spring-bullet?

Homework Equations

we are learning about the oscillations and energy. For this question I'm thinking I would need to use E= Kinetic energy + potential energy... (1/2)KA2=(1/2)mv² + (1/2)Kx²
but I don't know what to do to get started, I am soo lost!

The Attempt at a Solution

 

[Doc Al]

Start by finding the speed of the "bullet + block" immediately after the bullet embeds itself in the block. What's conserved during that 'collision'?

 

[Stonebridge]

I suggest using conservation of momentum on the collision between the bullet and block to find the initial velocity upwards of the block.

 

[Dotty21690]

thanks! but then how would I find part b? would I find the kinetic energy of the bullet and the mechanical energy of the system(in which I would plug back in my value for the amplitude?)

 

[Doc Al]

thanks! but then how would I find part b? would I find the kinetic energy of the bullet and the mechanical energy of the system(in which I would plug back in my value for the amplitude?)

Compare the KE before and after the collision.