Question: A 1-kg ball starting at h = 8.6 meters slides down a smooth surface where it encounters a rough surface and is brought to rest at B, a distance 15.8 meters away. To the nearest joule what is the work done by friction? Can you pls. help with this question? Do you need to find the potential energy and then work from there? potential E = mgy so you could find that... U = (1 kg) * (9.81 m/s) * (8.6 m) = 84.366 but how would I work it from there?