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# hw 15 - brown(twb493 hw 15 turner(57340 This print-out...

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brown (twb493) – hw 15 – turner – (57340) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A car with a mass of 1670 kg kg starts from rest and accelerates to a speed of 16 m / s in 14 . 1 s. Assume that the force of resistance remains constant at 356 . 8 N during this time. What is the average power developed by the car’s engine? Correct answer: 18014 . 7 W. Explanation: Let : m = 1670 kg , v f = 16 m / s Δ t = 14 . 1 s F r = 356 . 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)(16 m / s) 14 . 1 s + 356 . 8 N bracketrightbigg × 16 m / s 2 = 18014 . 7 W . 002 10.0points A car weighing 8300 N moves along a level highway with a speed of 72 km / h. The power of the engine at this speed is 69 kW. The car encounters a hill inclined at an angle of 7 . 9 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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