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Need help with kinetic energy calculation

  1. Oct 29, 2006 #1

    This seems like a helpful community so I thought I could ask you guys for some help.

    First of all I need to clarify that English is not my first language so you'll have to excuse me if I make any grammatical or spelling errors.

    Ok, here's my question:

    I'm am trying to calculate the kinetic energy of a person who is standing on a diving board 8 meters above the surface. He weighs 80kgs.

    What is his kinetic energy after falling 2m ?

    I think it's 1/2*80*9,8^2 = 3841,6 joule

    But the textbook tells me I have the wrong answer

    I also have to find out his velocity as he reaches the surface, and I have no clue where to even begin.

    Any help would be appreciated, thank you.
  2. jcsd
  3. Oct 29, 2006 #2


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    You appear to have used the ke equation, without knowing his velocity - where did you get 9'8 from??

    This is about conservation of energy.

    Calculate how much PE he loses in falling 2m.

    This is the ke he has after 2 metres.

    For the speed as he hits the water, calculate how much PE he has lost by this point, this gives you the KE. Work backwords to find the velocity.
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