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Homework Help: Work and power

  1. Jan 25, 2005 #1
    I used 165 watts to climb a set of stairs 3m high for 10s(550n*3m/10s). My electric company supplies 1kw for 1hr for 8 cents. If I climbed those stairs for 1 hour how much money would it be worth? I multiplied 165 by 360 divided by 1000 to get 59.4kw's. If I multiply 59.4 by .08 I get $4.75. Did I forget something?
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  3. Jan 25, 2005 #2


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    Since the problem does not specify the energy consumed for getting down a ladder (it can't be equal to the one for climbing)...I'd say that my answer is 13$ and 20รง.

  4. Jan 25, 2005 #3


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    I don't understand what you mean when you say "I used 165 watts to climb a set of stairs 3m high for 10s". A "watt" is a measure of power: energy per second. You can't 'use' a watt in the same way you would 'use' a Joule (or, for that matter, a "watt-second" or "kilowatt-hour").

    If you mean that you averaged 165 watts of power output for all the 10 seconds, then you produced 1650 "watt-seconds"= 0.00041666.. kilowat-hours. Working at that for a full hour, 360 of the 10 second units, you would have produced 0.15 kilowatt-hour, worth, at the rate you give, 1.2 cents.
  5. Jan 26, 2005 #4
    Thank's HallsofIvy! I should have converted joules to kwh's.
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