A spring with a spring constant of 10 N/cm has a cage attached to one end (Fig. 7-53). Taking rightward as the positive direction, (a) how much work does the spring force do on the cage when the spring is stretched from its relaxed length by 7.6 mm? (b) How much additional work is done by the spring force when the spring is stretched by an additional 7.6 mm?
The Attempt at a Solution
First, I changed the units.
a) W = ½*1000*x0.0076² = 0.02888 J
b) W = ½*1000*(0.0152² - 0.0076²) = 0.08664 J
I know that I did the right work but I am still wrong. Does the answer have to be negative? But the problem states that the right is positive. I can't find my mistake.