A wheel of mass 15kg and radius 1m is being pulled by a horizontal force F against a step 0.4m high. What initial force is jut sufficient to turn the wheel so that it will rise over the step?

Question

anonymous · Answer

Do u have answer key with u

anonymous · Answer

i got 120N

anonymous · Answer

It's supposed to be 200N

anonymous · Answer

Hmm, I'm getting about 250N . . .

anonymous · Answer

Hmm

anonymous · Answer

Are we assuming that the force is being applied through the center of the wheel?

anonymous · Answer

Ah, i think I know what I did wrong. The length of the lever arm is changing as the wheel climbs the step...

anonymous · Answer

mm torques should be equal .. look at the step edge
now the torques are due to Mg and F

|dw:1350057907922:dw|

length of A is 1-0.4 = 0.6
length of B is sqrt(1^2 - 0.6^2) = 0.8

so
0.6 * F = 0.8 * 150
F = 200