1. The problem statement, all variables and given/known data Ok, so first I find the tension on the top portion of the belt.. 3.0=T(100/1000) , T-> tension T=30N , though I'm not sure if taking the diameter of Q is correct. Then I find the torques on wheel P, which I multiply the tension with the radius (150/2 mm) which I get 4.5 Nm. But the correct answer is D. Judging by the correct answer, I assume that they used the radius of Q to find tension, not diameter.. But why radius? I thought torque is force multiply perpendicular distance separating the two forces?