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A level conservation of energy

  1. Aug 12, 2012 #1
    1. The problem statement, all variables and given/known data

    Using formulae for PE and KE, find the speed that a tennis ball hits the ground when dropped from 20m.

    2. Relevant equations

    m x g x h and 1/2 x m x v^2

    3. The attempt at a solution

    PE=KE

    Mgh = 1/2mv^2 (masses cancel out)
    9.8 x 20.= 1/2 v^2
    196 = 1/2 v^2
    196/ 1/2 = v^2
    392 = v^2
    V = 19.8(2dp) ms-1

    Am I correct? Thankyou
     
  2. jcsd
  3. Aug 12, 2012 #2

    CWatters

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    yes but what is the (2dp) in ..

    V = 19.8(2dp) ms-1

    Answer should just be

    V = 19.8 ms-1


    Allways better to rearrange the equation before putting in the numbers.
     
  4. Aug 12, 2012 #3
    Thankyou
     
  5. Aug 12, 2012 #4

    CWatters

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    Oh I see you mean two decimal places?
     
  6. Aug 12, 2012 #5
    Haha yeah 2dp, that's the English way (guessing your not English?)
     
  7. Aug 12, 2012 #6

    CWatters

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    Yes English (but was still awake at 2am last night so not on best form today :-).
     
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