So I have a constant force F acting tangentially on a mass m in a vertical circle around a loop of radius r. The mass starts from rest at the very top of the loop. The only other force is gravity, that is m*g Now I did Work=Change in energy with a system that is comprised of both the earth and mass. Here work is simply 2*pi*r*F. When I try to solve this by seperating this into two parts, finding velocity at the bottom of the loop using work energy thm then using that as the initial velocity for another work energy theorem setup, it didn't work. Why? Work energy theorem is supposed to work all the time. Gravity is conservative, so the results should be the same regardless. Any help would be appreciated. Thanks.