A thin, cylindrical rod ell = 20.4 cm long with a mass m = 1.20 kg has a ball of

Question

A thin, cylindrical rod ell = 20.4 cm long with a mass m = 1.20 kg has a ball of diameter d = 10.00 cm and mass M = 2.00 kg attached to one end. The arrangement is originally vertical and stationary, with the ball at the top as shown in the figure below. The combination is free to pivot about the bottom end of the rod after being given a slight nudge. After the combination rotates through 90 degrees, what is its rotational kinetic energy? J What is the angular speed of the rod and ball? rad/s What is the linear speed of the center of mass of the ball? m/s How does it compare with the speed had the ball fallen freely through the same distance of 25.4 cm? v swing is v fall by %.

Explanation / Answer

a) rotational kinetic energy = mgH = 1.20 x 9.81 x (0.204/2 - 0) + 2 x 9.81 x (0.05 +0.204) = 6.184 J

b) 6.184 = I2 /2

6.184 = (1.2 x 0.204^2 /3 + 2 x 2 x 0.05^2 /5 + 2 x 0.204^2)

= 60.70 rad/s

c) v = r = 60.70 x (0.204 + 0.05) = 15.41 m/s

d) (2 +1.2)vfall2 /2 = 1.2x 9.8 x (0.204/2) + 2 x 9.81 x (0.05 +0.204)

vfall = 1.97 m/s

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