I'm in introductory level mechanics and I was wondering if someone could give me a hand with this question:

A playground ride consists of a disk of mass

*M*= 56 kg and radius

*R*= 2.0 m mounted on a low-friction axle. A child of mass

*m*= 24 kg runs at speed

*v*= 2.3 m/s on a line tangential to the disk and jumps onto the outer edge of the disk. The child on the disk then walks inward on the disk and ends up standing at a new location a distance

*R*/2 = 1 m from the axle. Now what is the angular speed?

I calculated most, if not all, of the things that I think I need already, like the moments of inertia at R=2, the angular momentum when R=2, etc., but I don't know what expression I can use to find out the new angular speed of the child once he moves. I was thinking that if angular momentum stayed constant, I could calculate using the expression Ltotal = Ldisk + L child, since I can find all of the things needed, but that isn't giving me the right answer.

Sorry my question is a little long. Thank in advance for the help!