In Fig.7-11 http://edugen.wiley.com/edugen/courses/crs1650/art/qb/qu/c07/pict_7_11.gif we must apply a force of magnitude 82.0 N to hold the block stationary at x=-2.0 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) This is what I did, but can anyone confirm if it's correct? F = -kx 82 = -k(-2) 82 = 2k 41 = k Convert 8J aka 8N/m to .08N/cm because the final answer has to be in cm. U = 1/2kx^2 For positive: 82 + .08 = 1/2(41)x^2 solve for x .. 2.00cm For negative: 82 - .08 = 1/2(41)x^2 solve for x.. 2.00cm (has to have 3SF) Something doesn't seem right.. maybe I messed up in converting? Any help would be much appreciated.. thanks!