A horizontal 90 kg merry-go-round is a solid disk of radius 1.50 m and is started from rest by a constant horizontal force of 50.0 N applied tangentially to the edge of the disk. The kinetic energy of the disk after 3.00 s is

From the rigid object under a net torque model,          ∑ τ = lα → α = ∑ τl= FR12MR2 = 2FMR From the definition of rotational kinetic energy and the rigid object under constant angular acceleration model.      K = 12Iω2= 12I(ω1+αt)2          = 12Iα2t2 = (12MR2)(2FMR)2t2 = F2t2MSubstituting, K = (50.0 N)2(3.00 s)2 (90.0 kg) = 250 J