1. A child of mass 25kg stands at the edge of a rotating platform of mass 150kg and radius 4m. The platform with the child on it rotates with an angular speed of 6.2 rad/s. The child jumps off in a radial direction. (a) What happens to the angular speed of the platform? (b) What happens to the platform if, a little later , the child, starting at rest, jumps back onto the platform? (Treat the platform as a uniform disk) 2. I=1/2MR^2(platform) ; I=MR^2(child), L=Iω 3. My Attempt was to calculate the angular speed of the platform by using the fact that angular momentum is conversed. So two different inertias rotating at the same speed and then one of it leaves the system. Therefore the platform now has a different speed. But the solution I see in the book states that due to the fact that the child leaves the system in a radial direction the speed of the platform is NOT affected. How come? how is it important the direction? whether he leaves the platform radial or tangential the inertia is changed so the speed must be different. Why am I wrong, if I am?