1. The problem statement, all variables and given/known data A block of mass m lies on a surface thirty degrees above the horizontal. A force with a magnitude equal to twice the weight of the block pushes it uphill. If the coefficient of kinetic friction is 0.4, find the acceleration of the block. 2. Relevant equations Newton's laws of motion 3. The attempt at a solution Drew free body diagram: http://i.imgur.com/dA7MxvM.png If I choose my coordinate axes so that the x-axis is parallel to the ramp, ƩFy = 0 ƩFx = ma First the x-components: ƩFx = 2wsin60 - wsin60 - fk = ma I know that fk = μn, I know μ but don't know n. To find n from the y-components: ƩFy = n - 2wcos60 - wcos30 = 0 n = w(2cos60 + cos30) Substituting n into the x-component equation: ƩFx = 2wsin60 - wsin60 - μ(w(2cos60 + cos30)) = ma ƩFx = w(2sin60 - sin60 - 0.5cos60 + 0.25cos30) = ma 0.83w = ma Weight is the product of mass and acceleration due to gravity (0.83)mg = ma 0.83g = a a = 8.134 m/s^2 This question was on a small quiz I took today and although I don't have the answer with me, I remember seeing that the answer was near 7.8 and not 8.134. Where am I going wrong with this?