h15 - hernandez (ejh742) – homework 15 – Turner –...

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Unformatted text preview: hernandez (ejh742) – homework 15 – Turner – (58120) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A hot rod of mass 1300 kg, starting from rest reaches a speed of 110 m / s in only 15 . 9 s. What is the average output power? 1. . 494654 MW correct 2. . 0311103 MW 3. . 00899371 MW 4. . 989308 MW 5. . 000282821 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 = (1300 kg) (110 m / s) 2 2 (15 . 9 s) · mW 10 6 W = 0 . 494654 MW 002 10.0 points A car with a mass of 1 . 30 × 10 3 kg starts from rest and accelerates to a speed of 10.0 m/s in 13.8 s. Assume that the force of resistance remains constant at 342.7 N during this time. What is the average power developed by the car’s engine? Correct answer: 6423 . 64 W. Explanation: Let : m = 1 . 30 × 10 3 kg , v f = 10 . 0 m / s , Δ t = 13 . 8 s , and F r = 342 . 7 N . v f = a Δ t and Δ x = 1 2 a (Δ t ) 2 since v i = 0 m/s, and F = m a + F r , so P = F Δ x Δ t = F · 1 2 a (Δ t ) 2 Δ t = F a Δ t 2 = ( m a + F r ) v f 2 = parenleftBig m v f Δ t + F r parenrightBig · v f 2 = bracketleftbigg (1300 kg)(10 m / s) 13 . 8 s + 342 . 7 N bracketrightbigg × 10 m / s 2 = 6423 . 64 W . 003 10.0 points A car weighing 7900 N moves along a level highway with a speed of 78 km / h. The power of the engine at this speed is 57 kW. The car encounters a hill inclined at an angle of 9 . 7 ◦ with respect to the horizontal....
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This note was uploaded on 06/14/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.

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h15 - hernandez (ejh742) – homework 15 – Turner –...

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