Two people sit opposite each other on the edge of a rotating disk of radius, R, and negligible mass. One person has a mass of 40kg, the other of 50kg. The disk is rotating at 30 revs/min. What is the rotational kinetic energy if R=1.5m?

Rotational Kinetic Energy (KE) = (1/2) x Moment of Inertia (I) x (Angular Velocity (w) )²I=SUM(MR²) = 40 x (1.5)² + 50 x (1.5)² = 90 x (1.5)² = 202.5 kgm²w= 30 revs / min = 30 x (2π/60) = π (rad/s)KE= 0.5 x 202.5 x π² = 101.25 π²
KE= 999.297.... ~ 1000J