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Unformatted text preview: Homework 8help Chap. 13 (notice, you may have different value in your mastering physics) 13.6. Model: The magnetic computer disk is a rigid rotating body. Visualize: Solve: Using the rotational kinematic equation f i , t = + we get 1 = 0 rad + (600 rad/s 2 )(0.5 s  0 s) = 300 rad/s 2 = (300 rad/s) + (0 rad/s 2 )(1.0 s 0.5 s) = 300 rad/s The speed of the painted dot v 2 = r 2 = (0.04 m)(300 rad/s) = 12 m/s. The number of revolutions during the time interval t to t 2 is 2 2 2 1 1 1 2 2 1 1 2 1 1 2 1 1 1 ( ) ( ) 0 rad 0 rad (600 rad/s )(0.5 s 0 s) 75 rad 2 2 1 ( ) ( ) 2 1 rev 75 rad (300 rad/s)(1.0 s 0.5 s) 0 rad 225 rad (225 rad) 35.8 rev 2 rad t t t t t t t t = + + = + + = = + + = + + = = = 13.14 Visualize: The radius of the disk is 10 cm and the disk rotates on an axle through its center. Solve: The net torque on the axle is = F A r A sin A + F B r B sin B + F C r C sin C + F D r D sin D = (30 N)(0.10 m) sin ( 90 ) + (20 N)(0.05 m) sin 90 + (30 N)(0.05 m) sin 135 + (20 N)(0.10 m) sin 0 = 3 N m + 1 N m + 1.0607 N m = 0.939 N m Assess: A negative torque means a clockwise rotation of the disk. 13.22. Model: Two balls connected by a rigid, massless rod are a rigid body rotating about an axis through the center of mass. Assume that the size of the balls is small compared to 1 m. Visualize: We placed the origin of the coordinate system on the 1.0 kg ball....
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 Spring '10
 ZHOU

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