ps5c13 - Physics 111.01 October 3 2008 PS 5c(13 Problem 1 =...

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Physics 111.01 October 3, 2008 PS 5c (13) Problem 1 = Walker P 7-08. A child pulls a friend in a little red wagon with constant speed. If the child pulls with a force of 16 N for 14.4 m, and the handle of the wagon is inclined at an angle of 28 ° above the horizontal, how much work does the child do on the wagon? F m θ g Solution. "Work = force times distance." This means the component of the force in the direction of the motion: ( ) cos 16 N cos28 14.13 N Ff θ == ° = parallel to motion Then the work is equal to ( )( ) 14.13 N 14.4 m 203.4 J WF d = parallel to motion Problem 2 = Walker P 7-18. A 0.12 kg pinecone falls 15.5 m to the ground, where it lands with a speed of 16 m/s. g h m v (a) With what speed would the pinecone have landed if there had been no air resistance? (b) Did air resistance do positive work, negative work, or zero work on the pinecone? Solution. (a) We work this with the new work-into- energy method. 2 1 K m v 2 dm g h Solving for the velocity gives () 2 9.8 m/s 15.5 m 17.43 m/s = 2 2 vg h (b) Now, the actual speed was less, so the pine cone did not have as much energy as it would have without air resistance.
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ps5c13 - Physics 111.01 October 3 2008 PS 5c(13 Problem 1 =...

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