- #1
emmy
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Homework Statement
http://edugen.wiley.com/edugen/courses/crs4957/art/qb/qu/c07/pict_7_11.gif
In the above figure, we must apply a force of magnitude 82.0 N to hold the block stationary at x=-3.0 cm. From that position, we then slowly move the block so that our force does +8.0 J of work on the spring–block system; the block is then again stationary. What are the block's positions, in cm? ((a) positive and (b) negative)
Homework Equations
Fs=-kΔx
-kxo2-0.5kx2 = W
The Attempt at a Solution
I'm sort of lost when it comes to springs, but this is my best shot:
Fs=-kΔx
82N=-k(-3-0cm)
k=2733
W=-kxo2-0.5kx2
8J=-2733(-3)2- 0.5(2733)(x)2
8J=-24597-0.5(2733)(x)2
24605=-0.5(2733)(x)2
-18.01=x2
And that's where I'm stuck, so I definitely know it must be wrong. The only thing I can think is maybe I got the wrong sign on k, the spring constant. If so,
k=-2733
8J=2733(9)-0.5(-2733)(x)2
-17.99=x2
Either way, it's not a real number, so where did I go wrong...?