# Homework Help: Collision between two moving blocks with a spring

1. Oct 10, 2012

1. The problem statement, all variables and given/known data
A block of mass m1 = 4.0 kg slides along a frictionless table with a velocity of +10 m/s. Directly in front of it, and moving with a velocity of +3.0 m/s, is a block of mass m2 = 9.0 kg. A massless spring with spring constant k = 1120 N/m is attached to the second block as in the figure below. After the collision, the spring is compressed a distance X, find X.

(Attempt at a drawing)
block1 Spring.....Block 2
[m1] |--/\/\/\/[m2]

Everything is moving in the +x direction, or to the right.

2. Relevant equations
1/2*m*v^2
1/2*k*x^2
Pi=Pf
P=m*v

3. The attempt at a solution
I thought that you would use the difference between their KE's to find the PE stored in the spring. However, when I run the numbers into the equation PE = KE1-KE2. I end up getting slightly over. So I'm doing something wrong and I cannot find where it is at.

Edit: I accidentally hit backspace and reloaded the page, so it freaked out and copied everything.

2. Oct 10, 2012

### collinsmark

Welcome to Physics Forums!
If you want help, you're going to have to run the numbers and show us your work here. It's part of the forum rules.