(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

We must apply a force of magnitude 80N to hold the block stationary at x = -2.0cm. From that position, we then slowly move the block so that our force does +4.0J of work on the spring-block system; the block is then again stationary. What is the block's position? (Two answers.)

2. Relevant equations

F = -kx

W = (1/2)*k*xi^2 - (1/2)*k*xf^2

3. The attempt at a solution

80 = -k(-.02m)

k = 4000 N/m

With the spring constant, i plug it into the Work equation to find xf

4 = .5*4000*(-.02^2) - .5*4000*xf^2

3.2 = -2000xf^2

-.0016 = xf^2

And this is where I am stuck. The answer cannot be an imaginary number, but a real one. I know the equations are correct, so what am I doing wrong? Please explain.

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# Homework Help: Work done by a spring

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