1. Problem statement In figure, what magnitude of (constant) force F applied horizontally at the axle of the wheel is necessary to raise the wheel over an obstacle of height h=3.00cm ? The wheel's radius is r=6.00cm , and it's mass is m=0.800 kg. 2. Relevant equations Balance of forces: Fnet=0 (xy plane) Balance of torques: τnet=0 (z axis) 3. The attempt at a solution By balance of torques about point of contact with obstacle, F(r-h)=mgr I chose that point so as to not account for forces of contact there! The answer i got F=(mgr)/(r-h) F= 15.7 N The answer at the back of the text is 13.6N. What did i do wrong? Also i have this lingering doubt, will the normal forces at the point of contact with the horizontal floor , be included? I worked another problem where the solution i found ignored it and when i tried putting it in, it simply nullifies the weight , which lead to unreasonable answers... But still why is it not to be included? I mean it's also a force no.. Of course it disappears as soon as the wheel lifts off due to that horizontal F .. Thanks in advance..