A puck (mass m 1 = 4.95 kg) slides on a frictionless table as shown in the figur

Question

A puck (mass m1 = 4.95 kg) slides on a frictionless table as shown in the figure below. The puck is tied to a string that runs through a hole in the table and is attached to a mass m2 = 14.9 kg. The mass m2 is initially at a height of h = 14.9 m above the floor with the puck traveling in a circle of radius r = 3.96 m with a speed of 14.9 m/s. The force of gravity then causes mass m2 to move downward a distance 1.49 m.

(a) What is the new speed of the puck?
  m/s

(b) What is the change in the kinetic energy of the puck?
  J

Explanation / Answer

a) new radius r2 = 3.96 - 1.49 = 2.47 m

From conservation of angular momentum

m1 v1 * r1 = m1 v2 * r2

4.95 * 14.9 * 3.96 = 4.95 * v2 * 2.47

v2 = 23.89 m/s

b) Kinetic change = 1/2 m (v22 - v12)

= 0.5 * 4.95 [ 23.892 - 14.92 ]

= 863 J

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