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Math Help - Physical work done by force

  1. #1
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    Physical work done by force

    Weight of body 1 Kg
    Within 5 seconds the force that influenced the body was 20 Newtons.

    How much is physical work done by force ?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by totalnewbie View Post
    Weight of body 1 Kg
    Within 5 seconds the force that influenced the body was 20 Newtons.

    How much is physical work done by force ?
    There is not enough information here to determine the work done without
    making some assumptions about what has been omitted from the question.

    1. Assume you mean the body has mass of 1kg

    2. Assume the only force acting on the body is one of 5 N, acting for 5s

    3. Assume the body starts at rest.

    Then we have constant accelleration:

    a=f/m,

    so the velocity is:

    v=(f/m)t

    displacement from initial position is:

    s=(f/[2m])t^2

    Therefore with f=20\ \mbox{N}, m=1 \mbox{ kg}, and t=5 \mbox{ s}, we have:

    s=10 \times 25=250\mbox{ m}

    Therefore the work done is the force times the displacement =5000 \mbox{\ Joules}

    RonL
    Last edited by CaptainBlack; January 22nd 2007 at 09:14 PM. Reason: Correcting units error pointed out ny topsquark
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  3. #3
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    Correct answer!
    Thanks!

    But I started to think why gravitational forces are not involved ?
    For exmaple: F=ma+-mg
    Despite of constant acceleration gravitational forces F=mg influence that body.
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by totalnewbie View Post
    Correct answer!
    Thanks!

    But I started to think why gravitational forces are not involved ?
    For exmaple: F=ma+-mg
    Despite of constant acceleration gravitational forces F=mg influence that body.
    Well this could be taking place where the acceleration due to gravity has
    negligible effect over the time intervals in question.

    Alternatively it could be conducted on a low friction surface, where the
    normal reaction from the surface balances the gravitational force.

    RonL
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  5. #5
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by CaptainBlack View Post
    Therefore the work done is the force times the displacement =5000 \mbox{\ watts}
    Owie! The unit for work is "Joules."

    -Dan
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  6. #6
    Grand Panjandrum
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    Quote Originally Posted by topsquark View Post
    Owie! The unit for work is "Joules."

    -Dan
    Oppss..
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