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Power problem -- Mule pulling a wagon, convert work and power to time

  1. Jan 14, 2015 #1
    1. The problem statement, all variables and given/known data

    a mule is pulling a load of gold on a wagon. If the mules power output is 746 watts. if in a certain time interval the total work done by the team on the wagon was 23,500,000 j, how long was that interval of time
    2. Relevant equations
    I think its power = work divided by time

    3. The attempt at a solution
    I don't have one
  2. jcsd
  3. Jan 14, 2015 #2


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    Why don't you try to use power=work/time? What is a watt in units of joules? Just try.
  4. Jan 14, 2015 #3
    that's the thing, I don't know the numbers. The time isn't mentioned so I would have to re arrange the formula. My guess would be work times power or work divided by time. Like 746 times 746 times 23,500,000 or divided that. Im dumb and I can't figure it out.
  5. Jan 14, 2015 #4


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    I'll rearrange it for you. If power=work/time then time=work/power. I'm dumb is pretty weak excuse. You have to do something here. Now try and do it. Look things up if you have to.
  6. Jan 14, 2015 #5
    Would we have have to convert 746 watts into jouls? It would be 3,600,000. So will it be 23,500,000/3,600,000 = 1.44? Im sorry, it's not an excuse but it's hard for me to actually just sit down and think. Thats why I wont do AP physics next year.
  7. Jan 14, 2015 #6


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    Sorry, but if this one is a challenge then you probably shouldn't try AP physics. A watt is a joule/second. This is actually pretty elementary material. It's just dealing with basic algebra and physics units. I don't know what to say.
  8. Jan 15, 2015 #7


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    The formula you quoted was..

    power(W) = work(J) divided by time(S)

    So rearranging that gives..

    Time(S) = work(J) divided by power(W).
  9. Jan 15, 2015 #8


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    Mastering introductory physics is initially made a little more difficult because units of many quantities go by a number of names.

    The Joule is another name for a Newton.metre, and you can remind yourself of this by memorizing the formula W = F.s
    The Watt is another name for a Joule/second or a Newton.metre/second, this comes from the formula P = W/t

    So there is a second reason for memorizing formulae---not only are they needed for calculations, but once you realize how they also help you with the names of units, equations are immensely valuable tools of trade, whatever area of science you are dealing with.

    BTW, that 746 conversion factor is for hp to watts, but there is no mention of horsepower anywhere here. You are already given the mule's power in watts.
    Last edited: Jan 15, 2015
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