1. The problem statement, all variables and given/known data A block is at rest on a plank whose angle can be varied. The angle is gradually increased from 0 deg. At 26.5°, the block starts to slide down the incline, traveling 3.10 m down the incline in 2.00 s. Calculate the kinetic coefficent of friction between the block and the plank. 2. Relevant equations Uk = friction Coefficient D = Vot + 1/2at^2 F= ma kinetic Friction = cos(theta)*m*g*Uk 3. The attempt at a solution First i used the kinematic equation to solve for the acceleration, 3.1 = 0 + 1/2a(2)^2 a = 1.55 m/s^2 Then with the acceleration i got here pluged it in the F= ma to get, F = m (1.55) F = sin(theta)*m*g - cos(theta)*m*g*Uk Notice the m cancels out so i get Sin(theta)g-Cos(theta)*g*Uk= a g = 9.8m/s^2 I plugged everything in, theta = 26.5, a = 1.55, g = 9.8 and solved for Uk Uk turned out to be -.352 which is wrong and makes no sense... but nevertheless, .352 is also wrong. Any idea on what i did wrong? thanks for the help!