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# hw15(1) - lenoir(wml297 homework 15 Turner(58220 This...

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lenoir (wml297) – homework 15 – Turner – (58220) 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 1100 kg, starting from rest reaches a speed of 150 m / s in only 26 . 1 s. What is the average output power? 1. 0 . 00632184 MW 2. 0 . 948276 MW 3. 0 . 474138 MW correct 4. 0 . 0181662 MW 5. 0 . 000121108 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 = (1100 kg) (150 m / s) 2 2 (26 . 1 s) · mW 10 6 W = 0 . 474138 MW 002 10.0 points A car with a mass of 1 . 09 × 10 3 kg starts from rest and accelerates to a speed of 17.1 m/s in 18.1 s. Assume that the force of resistance remains constant at 310.4 N during this time. What is the average power developed by the car’s engine? Correct answer: 11458 . 5 W. Explanation: Let : m = 1 . 09 × 10 3 kg , v f = 17 . 1 m / s , Δ t = 18 . 1 s , and F r = 310 . 4 N . v f = a Δ t and Δ x = 1 2 a 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 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 (1090 kg)(17 . 1 m / s) 18 . 1 s + 310 . 4 N bracketrightbigg × 17 . 1 m / s 2 = 11458 . 5 W . 003 10.0 points A car weighing 8800 N moves along a level highway with a speed of 90 km / h. The power of the engine at this speed is 67 kW. The car encounters a hill inclined at an angle of 6 with respect to the horizontal. If there is no change in the power of the engine, and no change in the resistive forces acting on the car, what is the new speed of the car on the hill?

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hw15(1) - lenoir(wml297 homework 15 Turner(58220 This...

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