A 70 kg crate starting at rest slides down a rough ramp 4.0 meters long, inclined at 30 degrees above horizontal. At the bottom, it is moving at 5.0 m/s. what was the work done by friction on the crate??? Answers= A. -500 Joules B. 500 Joules C. 460 Joules D. -460 Joules E. 0.0 Joules I got this answer wrong and i was wondering why... so here is my work. i got the height to be 2meters by using sin 30 Mgh - Wf = 1/2MV^2 70 * 9.81 * 2 - wf = .5 * 70 * 5.0^2 875 - wf = 1373.4 wf =1373.4-875 wf = 500 joules so i got positive 500 joules. can any body tell me what the answer truly is and what i did wrong?? thank you alot!!