1. The problem statement, all variables and given/known data We have a body of mass M placed in a kind of sledge like on the picture: Coefficient of fristion between the mass and the sledge is zero, but the coefficient of friction between the wedge and the sledge is μ. Angle of the wedge is α. The sledge is massles. The slegde is pushed with some initial velocity up the wedge. What are the forces that the mass M acts with on the plates at the sides of the sledge? 2. Relevant equations Inertial force: F_I=-ma 2nd Newten s Law F=ma 3. The attempt at a solution If the sledge was not moving, the force acting on the left plate would be F=mg*sinα, but since it is moving, we calculate the acceleration down the wedge, which is: ma=mg*sinα+mgμ*cosα -> a= g(sinα+μ*cosα) So the resultant force is: F=mg*sinα-(mg*sinα+mgμ*cosα)=-mgμ*cosα and it points up the wedge. Is that right?