Card 42 / 46: A small hydroelectric dam produces 90 megawatts of power. If a typical home in the area can consume 20kW at peak usage, how many such homes can the hydroelectric plant supply at peak usage?
A)
5000
B)
450
C)
45,000
D)
45
E)
450,000
Answer:
A) 5000
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In words, the number (N) of houses is the total power (P) divided by the power per house (H), or N = P/H. Notice that the units cancel appropriately.
An easy way to to this calculation in your head is to remember that
X1 Xm = X1+m.
In the present case, 90/20 = 4.5 and 106 /103; =106-3 = 103.
The common mistakes you may make in this problem are misidentifying mega and kilo, using the wrong calculation (P/H), and misplacing a decimal point.
You may avoid these errors by:
1. Checking that the units cancel appropriately in your calculation:
P [power] / H [power/house] = N [house]
2. Checking your calculation for the proper order of magnitude (i.e. power of 10) by just adding the exponents in your head, as above.
This procedure is useful even if you use a calculator or computer.
Correct! The exact number is 4500, but 5000 is close enough.
Factor of ten off. Check exponents.
Factor of ten off. Check exponents.
Come on! A whole power plant for 45 houses? Check exponents and definitions of Mega and Kilo.
Check exponents and definitions of Mega and Kilo.
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Measurement & Experimentation Laboratory ME301
Author:
Dr.Steve GibbsProfessor
The Saylor Foundation
USA
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