A puck of mass m = 48.0 g is attached to a taut cord passing through a small hol

Question

A puck of mass m = 48.0 g is attached to a taut cord passing through a small hole in a frictionless, horizontal surface (see figure below). The puck is initially orbiting with speed vi = 1.20 m/s in a circle of radius ri = 0.320 m. The cord is then slowly pulled from below, decreasing the radius of the circle to r = 0.150 m.

(a) What is the puck's speed at the smaller radius?
m/s

(b) Find the tension in the cord at the smaller radius.
N

(c) How much work is done by the hand in pulling the cord so that the radius of the puck's motion changes from 0.320 m to 0.150 m?
J

Explanation / Answer

a) V1*r1 = V2*r2 ? V2 = V1 [r1/r2] = 1.20 [ 0.320 / 0.150 ] = 2.56 m/s b) T = m*V2²/r2 = .048 * 2.56²/.150 = 2.097 N c) W = dKE = ½m*(V2² - V1²) = .122 J

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