# ps6c16 - Physics 111.01 October 10, 2008 PS 6c (16) Problem...

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Physics 111.01 October 10, 2008 PS 6c (16) Problem 1 = Walker P 8-28. Catching a wave, a 75 kg surfer starts with a speed of 1.3 m/s, drops through a height of 2.05 m, and ends with a speed of 8.2 m/s. How much nonconservative work was done on the surfer? kJ Solution. We will calculate the total initial and final mechanical energy, T + U, of the surfer. If the final mechanical energy is less, then negative work was done. This is the usual case, when something like friction or other dissipation results in losing energy. However -- waves could in principle accelerate the surfer! We will have to see . . . . 1 2 v 1 v 2 y y=0 h () ( ) 11 1 2 1 1 2 2 2 1 2 75 kg 1.3 m/s 75 kg 9.8 m/s 2.05 m ET U mv mgh =+ 1570 J = ( 22 2 2 1 2 2 2 1 2 0 75 kg 8.2 m/s U mv ) 2521.5 J = + = = non-conservative 2 1 Aha! Positive non-conservative work was done on the surfer by the waves! 951 J=0.951 kJ WE E = −= Problem 2 = Walker P 8.29. At a playground, a 19.7 kg child plays on a slide that drops through a height of 2.01 m. The child starts at rest at the top of the slide. On the way down, the slide does a nonconservative work of -312 J on the child. What is the child's

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## This note was uploaded on 05/13/2010 for the course PHYSICS 111 taught by Professor Staff during the Fall '08 term at S.F. State.

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ps6c16 - Physics 111.01 October 10, 2008 PS 6c (16) Problem...

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