Lecture14

# Lecture14 - Power Power is the rate of which the work is...

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Power Power is the rate of which the work is done. The average power, equals to work W divided by time. Instantaneous power It is convenient to write instantaneous power in terms of force and velocity Unit is the watt (W) = 1J/s

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Calculate the power required of a 1400- kg car (a) the car climbs a 10⁰ hill at 80 km/h (b) the car accelerates along a level road from 90 to 110 km/h in 6 seconds. Assume that the average retarding force on the car is F r =700 N throughout. A) F = 700 N + mg.sin 10⁰ = 700 N + 2400 N = 3100 N P = F.v = 3100 N * (22 m/s) = 68000 Nm/s = 6800 Watts B) The car accelerates from 25 m/s to 30.6 m/s in 6 sec. a = (30.6 m/s 25 m/s)/ 6 s = 0.93 m/s 2 F = ma + F r = 1400 kg * 0.93 m/s + 700 N = 2000 N F is constant, but the velocity is not. P (W) t(s) F.v 0 F.v f = (F.v 0 +F.v f )/2 = 3100 N * (25 m/s +30.6 m/s)/2 Required instantaneous power increases with speed, and the minimum available power of the car must be equal to or more than the maximum instantaneous power required for this motion. P
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## This note was uploaded on 11/19/2010 for the course LECTURE 1 taught by Professor Yildiz during the Spring '10 term at Berkeley.

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Lecture14 - Power Power is the rate of which the work is...

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