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Unformatted text preview: alexander (jra2623) homework 14 Turner (92510) 1 This printout should have 12 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A hot rod of mass 1700 kg, starting from rest reaches a speed of 120 m / s in only 11 . 8 s. What is the average output power? 1. . 0879058 MW 2. . 000732548 MW 3. . 0172881 MW 4. 1 . 03729 MW correct 5. 2 . 07458 MW Explanation: The average output power is equal to the kinetic energy acquired divided by the total time, so P = 1 2 mv 2 t = (1700 kg) (120 m / s) 2 2 (11 . 8 s) mW 10 6 W = 1 . 03729 MW 002 10.0 points A car with a mass of 1 . 67 10 3 kg starts from rest and accelerates to a speed of 11.8 m/s in 17.9 s. Assume that the force of resistance remains constant at 337.8 N during this time. What is the average power developed by the cars engine? Correct answer: 8488 . 29 W. Explanation: Let : m = 1 . 67 10 3 kg , v f = 11 . 8 m / s , t = 17 . 9 s , and F r = 337 . 8 N . v f = a t and x = 1 2 a ( t ) 2 since v i = 0 m/s, and F = m a + F r , so P = F x t = F 1 2 a ( t ) 2 t = F a t 2 = ( m a + F r ) v f 2 = parenleftBig m v f t + F r parenrightBig v f 2 = bracketleftbigg (1670 kg)(11 . 8 m / s) 17 . 9 s + 337 . 8 N bracketrightbigg 11 . 8 m / s 2 = 8488 . 29 W . 003 10.0 points A car weighing 8900 N moves along a level highway with a speed of 77 km / h. The power of the engine at this speed is 71 kW. The car encounters a hill inclined at an angle of 8 . 8 with respect to the horizontal....
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 Summer '08
 Kaplunovsky
 Mass, Work

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