1. The problem statement, all variables and given/known data See post #3 Assume the YoYo is a solid cylinder with mass M and radius R for all parts!!!!! 2. Relevant equations Lots? 3. The attempt at a solution Part A - Find the moment of inertia about the center of mass and the point of contact with the ground: ICOM = 1/2 MR2 IIPoC = 1/2 MR2 + MR2 = 3/2 MR2 by parallel axis theorem Part B - Calculate the torque on the Yoyo about the center of mass, and the net horizontal force. Torque = r x F = rF since r is perp to F Fnet x = F cos θ Part C - What is the angular accel. of the yoyo about its center of mass? Linear acceleration? Torque = rF = Iα α = rF/I α = 2rF/MR2 and since alin = αr a = 2r2F/MR2 Part D - Find the net torque about the instantaneous point of contact Ok heres where I get stuck. Torque = rF sin σ , where σ is the angle between the applied force F and the r vector, right? Well no joke the geometry is complex. I cant find any way to get the angle between these two, here's what I've got so far: σ is the angle between the two blue lines, which represent the force and the r vector. Ive also extended the force line so you can see the line of action, if it helps. Any help would be greatly appreciated!