What minimum force F applied horizontally at the axle of the wheel is necessary to raise the wheel of mass M and radius R over a step of height H. A picture for this is at http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=128765607&imageID=1460005538 The answer key says that the correct answer is F =[mg*SQRT(2RH-H^2)]/r-h I know that mg is gravity so the force of gravity plays a role here. I don't know the direction of friction because F is pointing right, but the object also rotates clockwise. Friction would resist the sliding but would contribute to the rotation. I know torque is the cross product of R and F. I have no idea though why we have SQRT(2RH-H^2). I don't know what to do. Am I suppose to work with torque somehow?