A 2.0-kg block slides down a fixed, rough curved track. The block has a speed of 5.0 m/s after its height above a horizontal surface has decreased by 1.8 m. Assume the block starts from rest. How much work is done on the block by the force of friction during this descent?
1) -14 J
2) -12 J
3) -10 J
4) -16 J
5) -25 J
Answer: 3