## Find minimum force to raise wheel

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/inde...eID=1460005538

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?
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 Recognitions: Homework Help Take moment about the contact point, and use a force with unknown direction for the reaction at the contact point.
 I am not sure about this...is the moment of inertia with respect to the contact point MR^2 + R^2 with the parallel axis theorem? I know that whatever force the wheel pushes against the contact point, the same force will push the wheel back. But I am not sure about how to find that force for the reaction.

Recognitions:
Homework Help

## Find minimum force to raise wheel

By moment, i meant sum of torque, and consider Normal force = 0.
 With net torque, I have mg*R + F(R-H). So F = mg*R/(R-H) From the way it seems, I got the F(R-H) part right, but mg*R is still not quite right. HOw do I get SQRT(2RH-H^2)?

Recognitions:
Homework Help
 Quote by vu10758 With net torque, I have mg*R + F(R-H). So F = mg*R/(R-H) From the way it seems, I got the F(R-H) part right, but mg*R is still not quite right. HOw do I get SQRT(2RH-H^2)?
Your lever arm for the weight is wrong, REMEMBER THE LEVER ARM IS PERPENDICULAR TO THE LINE OF ACTION OF THE FORCE.