# Homework Help: Mass-spring extensions HELP

1. Oct 9, 2008

### kay123

Mass-spring extensions HELP!!!

I'm writing a paper on one of my lab experiments and I'm not sure my physic concept is right? The question asks if the mass of a cart affects the extension of the spring. A spring is attached to a cart which is attached to sting through a pulley and connected to a hanging object of mass W (a picture is attached). From my results, the spring stretched slightly more with the cart than with out the cart attached to the spring.

I know that at equilibrium all forces equal 0. Σ Fx = Σ Fy = 0
Fs= kx
F=mg

(with cart)
Σ Fx = Fs –Th
Σ Fy = Tv + Fn - Mgw -Mgc

(without cart)
Σ Fx = Σ Fx = Fs –Th
Σ Fy = Tv - Mgw

If k is constant and Fs= kx and F=mg then mg=kx. Then if the cart was attached, mass will increase, therefore x (the spring extension) will increase, which explains why the spring stretched more when the cart was attached.

Is this somewhat right? (I know this is wrong, because i got my paper back saying it was the wrong concept) So can you help me? Am I missing something?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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