The puck in the figure below has a mass of 0.220 kg. Its original distance from

Question

The puck in the figure below has a mass of 0.220 kg. Its original distance from the center of rotation is 40.0 cm, and it moves with a speed of 85.0 cm/s. The string is pulled downward 15.0 cm through the hole in the frictionless table. Determine the work done on the puck. (Hint: Consider the change of kinetic energy of the puck.)
J

The puck in the figure below has a mass of 0.220 kg. Its original distance from the center of rotation is 40.0 cm, and it moves with a speed of 85.0 cm/s. The string is pulled downward 15.0 cm through the hole in the frictionless table. Determine the work done on the puck. (Hint: Consider the change of kinetic energy of the puck.)

Explanation / Answer

initially   v = 85 cm/s = 0.85m /s
T = mv^2 /r   = 0.220 x 0.85^2 / 0.40 =0.397 N
finally ,
T = mvf^2 / r
0.397 = 0.220 x vf^2 / (0.40 - 0.15)
vf = 0.672 m/s
work done = 0.220 x (0.672^2 - 0.85^2) /2 = -0.02985 J

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