Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

384 Chapter 13 Energy and Power

The minimum energy requirement for this task is equivalent to providing electricity to fifteen

100-W light bulbs for 1 minute (90,000 J). Next time you feel lazy and are thinking about tak-

ing the elevator to go up one floor, reconsider and think about the total amount of energy that

could be saved if people would take the stairs instead of taking the elevator to go up one floor. As

an example, if 1 million people decided to take the stairs on a daily basis, the minimum amount

of energy saved during a year, based on an estimate of 220 working days in a year, would be

We will revisit this problem, after we discuss efficiency, to determine the amount of fuel

needed in a power plant to provide the amount of energy that we just calculated in Example 13.6.

 66  10

9

J660 GJ

energy savingsa

90,000 J

30 persons

ba

1

day

b11,000,000 persons 21 220 days 2

Example 13.7 Determine the power required to move a person who weighs 220 lb a vertical distance of

2.5 ft in 1 s.

Therefore, 1 horsepower represents the power required to lift a person weighing 220 lbf, a dis-

tance of 2.5 ft in 1 second. There are a number of other ways to think about what 1 horsepower

physically represents. It could also be interpreted as the power required to lift an object weight-

ing 100 lbfa distance of 5.5 ft in 1 second. How powerful are you?

power

work

time



1 220 lbf 21 2.5 ft 2

1 s

 550

lbf#ft

s

1 hp

Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀