1. The problem statement, all variables and given/known data The height of the slope shown in the figure is 30 cm, and its base is 40 cm. A solid cylinder of uniform density, which has the same mass as the slope, rolls down along the slope without slipping. What is the least value of the coefficient of friction between the inclined plane and the horizontal ground if the slope does not slip? 2. Relevant equations 3. The attempt at a solution I understand that this is a simple problem but I cannot reach the specified answer though I did a similar problem recently. The forces acting on the wedge are the normal reaction from cylinder (N), normal reaction from ground (N'), weight (mg) and the frictional force (f). Balancing forces on the wedge in the vertical direction: $$N'=mg+N\cos\theta$$ where ##\theta## is the angle made by the slope with the horizontal. Since the wedge doesn't slip, $$f \geq N\sin\theta \Rightarrow \mu N' \geq N\sin\theta$$ Using ##N=mg\cos\theta## and solving the equations, I don't get the right answer. Any help is appreciated. Thanks!