What Was Wrong with My Spring Compression Calculation?

[madah12]

Homework Statement

there is a problem in my final that I can't actually remember the values of the variables but I got 1 out of 4 grade in it and I was wondering what's wrong with my solution

I am just going to write the variables because I don't know the numbers:

a spring compressed equal distances by two boxes of the same mass the spring is not attached to the boxes when it is released one of the boxes moves with a velocity v calculate the total compression distance of the spring

Homework Equations

The Attempt at a Solution

by the conservation of momentum v₁=-v₂ and they have the same magnitude
E1=E2
.5k x_T^2= .5m(v₁)^2 + .5m(v₂)^2= mv^2
x_T=((2mv^2)/k)^.5

(v_1 ,m and k are given and the spring's mass is negligible )

 

[madah12]

I am very bad at paint ,but I tried to draw their picture
http://img155.imageshack.us/i/springz.png/

 

[cupid.callin]

Well your answer looks good

you must have done some mistake in calculation

 

[madah12]

yes I thought so too I did it so fast I didn't revise the calculations