In the figure, a 900-kg crate is on a rough surface inclined at 30° . A constant external force of 7200 N is applied horizontally to the crate. While this force pushes the crate a distance of 3.0 m up the incline, its velocity changes from 1.2 m/s to 2.3 m/s. How much work does friction do during this process? the teacher said it is -3730 J how is that?