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Homework Help: Work Energy and Power Question

  1. Nov 10, 2009 #1
    Thanks in advance, I just want to double check!

    1. The problem statement, all variables and given/known data

    A 5 kg ball is tossed into the air with an initial velocity of 6m/s.
    a) What is the kinetic energy of the ball?
    b) If the power delivered to the ball was 100watts, over what time interval did
    the power delivery occur?

    2. Relevant equations

    K.E = 1/2 mV*2

    P = E/t

    3. The attempt at a solution

    a)... using K.E = 1/2 mV*2 answer is 90J

    b)... using P = E/t answer is 0.9s
  2. jcsd
  3. Nov 10, 2009 #2

    Doc Al

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    Staff: Mentor

    Looks good!
  4. Nov 10, 2009 #3
    But I am a bit confuesd, is initial velocity is equal to velocity in the equation?In other words, can we plug the value of initial v in v in the equation? Shouldn't we try to get velocity?
  5. Nov 10, 2009 #4

    Doc Al

    User Avatar

    Staff: Mentor

    The velocity is given. It's the velocity of the ball immediately after leaving the hand.
  6. Nov 10, 2009 #5
    Thanks for the replies
  7. Nov 10, 2009 #6
    Now I get it. :) Thanks! I am having difficulty with treating problems related to kinetic energy and power.
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