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Homework Help: Kinetic energy

  1. Jan 21, 2007 #1

    soulja101

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    1. The problem statement, all variables and given/known data
    A 2.0 kg mass is fired straight up with a intial velocity of 60.0m/s
    A) wat is the kinetic energy when its 20.0m above the ground
    B)wat is the changhein height when its speed changes from 50m/s to 40m/s


    2. Relevant equations
    Ek=mv2/s



    3. The attempt at a solution
    A)EK=mv2/2 B)i didnt get question B
    =2.0kg*60.0ms
    =3600J
     
    soulja101, Jan 21, 2007
  2. jcsd
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  3. Jan 21, 2007 #2

    cristo

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    Well, for (a) you have calculated the kinetic energy of the mass as it leaves the ground. This is not the answer to the question, but it will help. Do you know how to calculate potential energy at a height h above the ground? Can you say anything about the sum of the potential and kinetic energies of the mass at any one point throughout its flight?

    edit: of course there are many ways to do the problem, as Kurdt points out below! Pick which one you prefer.
     
    Last edited: Jan 21, 2007
    cristo, Jan 21, 2007
  4. Jan 21, 2007 #3

    Kurdt

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    This is more to do with the kinematic equations than anything else. What will the speed be at 20m above ground level and thus what will the kinetic energy be. Then part b is obtained directly from one of the kinematic equations.
     
    Kurdt, Jan 21, 2007
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