I've attached a screenshot of the question. This is what i've tried so far: I've calculated the initial energy of the system (which is all potential energy): Energy of disc: 0.5*I*w^2 + 0.5 *m*v^2 + m*g*h = 0 + 0 + 0 Energy of arm: 0.5*m*v^2 + m*g*h = 0 + 4*9.81*1.5Cos(45) = 41.62 joules Energy of collar: 0.5*m*v^2 + m*g*h = 0 + 1*9.81*3Cos(45) = 20.81 joules Then i moved time on until the supporting arm BC was horizontal and calculated the energy at that stage (which would be all kinetic). When i do that, i end up calculating that the speed of the collar is 1.04 m/s. However, the answer is supposed to be 7.315 m/s. I'm doing something wrong, but i can't figure out what it is. Any hints on how this is supposed to be solved would be great. Thanks.