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## Work, Power, and Efficiency

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### Work, Power, and Efficiency Work is the transfer of energy that results from applying a force over a distance if nothing moves, no work was done unit of measurement ... – PowerPoint PPT presentation

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Title: Work, Power, and Efficiency

1
Work, Power, and Efficiency
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Work
• is the transfer of energy that results from
applying a force over a distance
• if nothing moves, no work was done
• unit of measurement is the Joule (J)
• used to be a Newton-meter (Nm)
• (this is about equal to lifting quarter pounder
up 3 ft in a second)

4
Work formula
W F D
W work F force D distance
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Example problem
• How much work is done when an object with a force
of 60 Newtons is moved a distance of 7 meters?

given formula
set up problem answer w/ unit of
measurement
F 60 N WFD 60N(7m)
420 Joules D 7 m
8
• There are different ways to get work done, but
regardless, the work must be done.
• Work Force x Distance
• Work Force x Distance

9
What is the difference?
3 m
3 m
10
Power
• how fast work is being done
• unit of measurement is the watt (W)
• James Watt, a Scottish engineer, invented the
steam engine.
• James Watt explained power as the number of
horses his engine could replace
• large quantities of power are measured in
kilowatts (kW)
• 1000 W 1 kW
• Americans often use horsepower
• 1 horsepower 746 watts

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Power formula
P W/T
P power W work T time
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Example problem
• A motor does 500 Joules of work in 5 seconds.
How much power does the motor have?

given formula
set up problem answer w/ unit of
measurement
W 500 J PW/T 500 J / 5 sec.
100 watts T 5 sec.
16
Efficiency
• the comparison of work put into a machine to the
work you get out of the machine.
• Work input (WI ) is the work that goes into a
machine
• Work output (WO ) is the work done by a machine
or the work you get out of the machine
• machines are always less than 100 efficient
because of friction
• however, they still help us by often reducing the
amount of force we put in by increasing the
distance we put in

17
Efficiency formula
Efficiency WO (100) WI
E Efficiency WO Work Output WI Work Input
18
Example problem
• What is the efficiency of a machine that produces
150 Joules of work when 160 Joules of work is put
into it?

given formula
set up problem answer w/ unit
of measurement
WO 150J E WO(100) 150J/160J(100)
94 WI 160J WI