# momentum

posted by .

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 230 kg and a radius of 1.6 m. A 38- kg child rides at the center of the merry-go-round while a playmate sets it turning at 0.15rpm. If the child then walks along a radius to the outer edge of the disk, how fast will the disk be turning (in rpm)?

i am aware that another question has been posted that is exactly the same as this, but when i used that technique, it did not work for me, so i am posting this question again. like i said, i need to get this answer in RPM and NOT rad/s

• momentum -

Convert rpm to rad/s to do the problem using conservation of angular momentum. Covert back to rpm when you get the answer. The child increases the moment of inertia by walking to the outer edge of the disk. I assume you know the formula for the moment of inertia of the disk

• momentum -

i tried that, but i'm not getting the answer right
i did disk momentum=Iw
and boy momentum=m*rpm*2pi/60
then i set those two equal to each other and then changed the w back to rpm, but i'm not getting the right answer.