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Figure 8-3.-A prony brake. | Up
Basic Machines - Intro to machines and motion theories | Next
Chapter 9 Force and Pressure |
equal to the circumference of the pulley times the
number of revolutions or 3.14 x 1 x 1,800 = 5,652 ft.
You know that the motor is exerting a force of
20 pounds through that distance. The work done in
1 minute is equal to the force times the distance, or
work = F x D = 20 x 5,652 = 113,040 ft-lb/min.
Change this to horsepower:
113,040
33,000
= 3.43 hp
Two common motor or engine ratings with
which you are familiar are the 1/16-hp motor of an
electric mixer and the 1/4-hp motor of a washing
machine.
SUMMARY
Remember two important points about power:
Power is the rate at which work is done.
Horsepower is the unit of measurement by which
power is equivalent to 33,000 foot-pounds of
work per minute, or 550 foot-pounds per
second.
8-4
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