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Math Help - Mechanics: Potential energy

  1. #1
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    Mechanics: Potential energy

    Very basic but i don't understand it...
    A particle of mass 2kg falls freely from rest. Calculate kinetic energy when it has descended 20 meters.
    Answer is 392J and i get 392000J.

    But i just did 2000(weight) x 9.8(gravity) x 20(distance)
    And i think thats wrong...well it must be because the answer i have is wrong lol.

    Any help please?
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  2. #2
    MHF Contributor
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    Hi

    The weight must be expressed in kg and not in g
    BTW gravity is 9.8 N/kg ...
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  3. #3
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    Quote Originally Posted by running-gag View Post
    Hi

    The weight must be expressed in kg and not in g
    BTW gravity is 9.8 N/kg ...
    tyvm
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by AshleyT View Post
    Very basic but i don't understand it...

    Answer is 392J and i get 392000J.

    But i just did 2000(weight) x 9.8(gravity) x 20(distance)
    And i think thats wrong...well it must be because the answer i have is wrong lol.

    Any help please?
    the unit of mass (not weight) is the kg not the gm, so that should be:

    2(mass) x 9.8(gravity) x 20(distance)

    CB
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