1. The problem statement, all variables and given/known data A box of mass m with an initial velocity of v0 slides down a plane, inclined at θ with respect to the horizontal. The coefficient of kinetic friction is μ. The box stops after sliding a distance x. How much work is done by friction? 2. Relevant equations Work=Force*x*cosθ W=ΔKE KE0=(.5)(m)(v02) 3. The attempt at a solution FF=(μ)(FN) FNety=FN-Fgy 0=FN-Fgy FN=Fgy Fgy=mgcosθ FFK=(μ)(FN) FFK=(μ)(mgcosθ) Work=Force*x*cosθ Work=(μ)(mgcosθ)*x*cosθ Something tells me this is not correct... To be honest I'm completely lost on this one =( Thats as close as I could get, and its not one of the answer choices. I'd be really thankful for anyone who could help show me the process of deriving the work done by friction!