A playground merry-go-round has a disk-shaped platform that rotates with negligible friction about a vertical axis. The disk has a mass of 240 kg and a radius of 1.4 m. A 33- kg child rides at the center of the merry-go-round while a playmate sets it turning at 0.20rpm. If the child then walks along a radius to the outer edge of the disk, how fast will the disk be turning?

Question

A playground merry-go-round has a disk-shaped platform that rotates with negligible  friction about a vertical axis. The disk has a mass of 240 kg and a radius of 1.4 m. A 33- kg child rides at the center of the merry-go-round while a playmate sets  it turning at 0.20rpm. If the child then walks along a radius to the  outer edge of the disk, how fast will the disk be turning?

bobpursley · Answer

conservation of momentum applies, in this case, angular momentum.

Diskmomentum=I*w
Boy momentum=33*r*2PI*.2/60

set them equal, w will be in rad/sec

disk moment of inertial is 1/2*240*r if you didn't know. Thin disk.

kate · Answer

the answer has to be in rpm, so does that mean that i'm not supposed to multiply by 2PI/60?