Posted by **Anonymous** on Sunday, December 5, 2010 at 3:37pm.

I need help with part b... I found in part a that delta L is .29568m and I think I might be doing something wrong with the units because I can't get the right answer.

A 156 g hockey puck is attached to a rubber band and rotated with an angular speed of 12.8 rad/s on frictionless horizontal ice. It takes a force of 1.12 N to stretch the rubber band by 1 cm.

(a) If the original length L of the rubber band is 1 m, by how much (in m) will it be stretched by the rotation?

Delta L = .29568m

(b) How much energy do you need to start the stone from rest and rotate as in part (a) with an angular speed of 12.8 rad/s? Neglect the mass of the rubber band.

Etotal = J

HELP: Add up the kinetic energy and the elastic potential energy.

HELP: Ekin = 1/2*m*v2, with v = length*omega.

Remember again to use the stretched length:

Eelast = 1/2*k*(Delta L)2

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