234_Physics ProblemsTechnical Physics

234_Physics ProblemsTechnical Physics - 236 Potential...

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236 Potential Energy Additional Problems P8.48 The potential energy of the block-Earth system is mgh . An amount of energy µθ k mgd cos is converted into internal energy due to friction on the incline. Therefore the final height y max is found from mgy mgh mgd k max cos =− where d y mgy mgh mgy k = ∴= max max max sin cot θ Solving, y h k max cot = + 1 . y max h FIG. P8.48 P8.49 At a pace I could keep up for a half-hour exercise period, I climb two stories up, traversing forty steps each 18 cm high, in 20 s. My output work becomes the final gravitational energy of the system of the Earth and me, mgy = 85 9 80 40 0 18 6 000 kg m s m J 2 bg ej a f .. making my sustainable power 6000 10 2 J 20 s W = ~. P8.50 v == 100 27 8 km h m s . The retarding force due to air resistance is RD A v = 1 2 1 2 0330 120 250
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