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A 70 kg cyclist develops 210 watts of power while pedaling at a constant velocity of 7.0 meters per seconds east What average force is exerted eastward on the bicyclist to maintain his constant speed?
Wiki User
∙ 13y ago
A convoluted but clever question, designed to really test one's comprehension
of some basic concepts.
The cyclist's kinetic energy is [ 1/2 M V2 ] = [ 35 x 49 ] = 1,715 joules. This fact
has no applicability whatsoever to the solution of this question.
Ordinarily, in the simplified world of basic physics, air resistance and other dissipative
factors are neglected, and no force is required to maintain constant velocity. But here,
it's pretty clearly implied that the cyclist and his machinery are leaking energy to the
surroundings, and he has to keep coming up with more energy just to keep moving
at constant speed in a straight line. We're even told that the rate of energy loss is
210 watts = 210 joules per second.
Energy delivered to the system in the form of mechanical work is quantitatively equal to (force) x (distance).
The rate at which the work is delivered is (force) x (distance/time) = (force) x (speed).
We know the rate (210 joules per second), and we know the speed (7 meters per second).
Work/time = Power = Force x speed
210 = F x 7
F = 210/7 = 30 newtons . (about 6.75 pounds of force)
Wiki User
∙ 13y ago
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