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Quiz 3B DL SEC _ _ Grade: 04/26/10 Last 6 digits of student ID _ _ _ _ _ _ Last name, first name: ________________ ________________ First three letters of your last name _ _ _ Useful formulae: Δ E TOT = Q + W; Δ E th = mc Δ T; Δ E bond = ±| Δ m Δ H|; Δ PE grav = mg Δ h; Δ KE tr = ½ m Δ v 2 ; Δ PE ms = ½ k Δ x 2 Useful constants: g=9.8 m/s 2 1. A skier skis down a mountain slope as shown below, beginning with a certain speed v i . Suppose you can entirely neglect the effects of friction and air resistance. a) ) Can you change the speed at the bottom by increasing the mass, m , of the skier (without changing the height h or θ )? If so, how? If not, why not? Explain. You will be graded on the completeness and the quality of your explanation. No you cannot. Δ PE + Δ KE = 0 mg Δ h + 1/2m(v f 2 – v i 2 ) = 0 g Δ h + 1/2(v f 2 – v i 2 ) = 0 so the masses cancel out. Changing the mass has no effect. b) If the 60 kg skier is then initially at rest, and begins skiing down the slope from an initial height of 300 m,
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This note was uploaded on 05/12/2010 for the course PHY 7 taught by Professor Staff during the Spring '08 term at UC Davis.
- Spring '08