A puck (mass m 1 = 1.35 kg) slides on a frictionless table as shown in the figur

Question

A puck (mass m1 = 1.35 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 = 4.1 kg. The mass m2 is initially at a height of h = 4.1 m above the floor with the puck traveling in a circle of radius r = 1.08 m with a speed of 4.1 m/s. The force of gravity then causes mass m2 to move downward a distance 0.41 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)

r1 = initial radius = 1.08 m

r2 = final radius = r1 - 0.41 = 1.08 - 0.41 = 0.67 m

v1 = initial speed = 4.1 m/s

v2 = final speed

Using conservation of angular momentum for puck

m v1 r1 = m v2 r2

4.1 x 1.08 = v2 (0.67)

v2 = 6.61 m/s

b)

change in KE = (0.5) m (V22 - V12) = (0.5) (1.35) (6.612 - 4.12) = 18.15 J

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