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hw14 - alexander(jra2623 homework 14 Turner(92510 This...

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alexander (jra2623) – homework 14 – Turner – (92510) 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 1700 kg, starting from rest reaches a speed of 120 m / s in only 11 . 8 s. What is the average output power? 1. 0 . 0879058 MW 2. 0 . 000732548 MW 3. 0 . 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 car’s engine? Correct answer: 8488 . 29 W. Explanation: Let : m = 1 . 67 × 10 3 kg , v f = 11 . 8 m / s , Δ t = 17 . 9 s , and F r = 337 . 8 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 (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. 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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