A bug that has a mass mb = 4 g walks from the center to the edge of a disk that is freely turning at 32 rpm. The disk has a mass of md = 12 g.

Question

If the radius of the disk is R = 28 cm, what is the new rate of spinning in rpm?

Answer 1

So Mr. M.,

Angular momentum is conserved here, too. One assumes zero initial angular momentum for the insect, although that may not necessarily obtain in reality. And, you must also assume that the insect does not exert any lateral forces as it radializes, otherwise you couldn't solve. So assume that the insect does the equivalent of arrive at the edge and then undergo inelastic impulse to latch onto the disc edge. Now all you need is the equation for angular momentum of a disc. If you aren't so quick to solve that as an integral (?? hmm...), look it up.

-- Cheers, --Mr. d.