Example 11.5 help needed with final part of the problem Estimate the magnitude o

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Example 11.5 help needed with final part of the problem

Estimate the magnitude of the angular momentum of a bowling ball spinning at 17 rev/s as shown in the fiqure. SOLVE IT Conceptualize Imagine spinning a bowling ball on the smooth floor of a bowling alley. Because a bowling ball is relatively heavy, the angular momentum should be relatively large. Categorize We evaluate the angular momentum, so we categorize this example as a substitution problem. We start by making some estimates of the relevant physical parameters and model the ball as a uniform solid sphere. A typical bowling ball might have a mass of 7.0 kg and a radius of 12 cm 3 A bowling ball that rotates about the z axis in the direction shown has an anqular momentum L in the positive z direction. If the direction of rotation is reversed, L points in the negative z direction Evaluate the moment of inertia of the ball about an axis through its center: 1= (2/5)MR2-(2/5)(7.0 kg)(0.12 m)2 0.040 kg·m2 Evaluate the magnitude of the angular momentum from the equation L,-to = (0.040 kg . m2)(17 rev/s)(2 rad/rev) = 4.27 kg m2/s Because of the roughness of our estimates, we should keep only one significant figure, so 4.0 MASTER IT HINTS GETTING STARTED I IM STUCKI Estimate the angular momentum of a car tire (with hub) about its center on a car that is traveling at 45 mph. Use 20 kg for the mass of the tire with hub and assume that the center of the wheel is at a height of 25 Cm L = 101 kg-m2/s

Explanation / Answer

angular momentum L = mvR

mass m = 20kg

radius R = 25 cm/2 = 0.125 m

speed v = 45mph = 45*1609.34/3600 = 20.11 m/s

angular momentum L = 20*20.11*0.125 = 50.29 kg-m^2/s

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