A toy car of mass M rolls down a frictionless ramp of height H > 2R and makes a circular loop of radius R at the bottom. (a) What is the car's speed at the bottom of the loop (b) at the top of the loop? (c) What is the force exerted by the track at the top of the loop? (d) What is the minimum value of H such that the car goes around the loop without falling off due to gravity? The first two parts are simple. a) Ei = MgH = Ef = 1/2Mv^2 solve for v b) Ef = 1/2Mv^2 + 2MgR = Ei solve for v But then.... c) The best I can do for this is figure that the track should exert a force downward on the car at the top of the track. So the forces acting on the car are Fnet = mg + Ft = ma, where Ft is the force exerted by the track. If I could find a, I could find Ft. But I can't do either. I haven't even tried part d yet. Help, anyone?