Quiz2_sol - 7A-C/D Win 09 Quiz 2 DL Sec Last 6 digits ID #...

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7A-C/D Win 09 Quiz 2 DL Sec Last 6 digits ID # Name (Last, First) Grade 1. A skier begins sliding down a hill from an initial stop at a height of 30 m. a) If we ignore any air resistance or friction from the snow, how fast would the skier be moving when she reaches a height of 20 m? Justify fully your answer. Initial: KE = 0, PE = mgh i = m*g*30 Final: KE = ?, PE = mgh f = m*g*20 No air resistance/friction, so only KE and PE energy systems change, and system is closed. Δ KE + Δ PE = 0 => KE f - 0 + mg(20-30) = 0 1/2 mv f 2 + m(10)(-10) = 0 v f 2 = 200, v v = 14.1 m/s b) In a more realistic problem, we can't ignore friction. Suppose the skier has reached 10 m/s speed at a height of 20 m, and still is traveling 10 m/s at the bottom of the hill. Write down (and explain how you got it) an energy conservation equation describing the skier's path from 20 m to the bottom of the hill. Numerical values aren't necessary but you must indicate whether each term is a positive or negative number. Pick initial point at height of 20 m, final at height of 0 m.
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This note was uploaded on 09/13/2010 for the course PHY 7A 56192 taught by Professor ? during the Winter '09 term at UC Davis.

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