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Kinetic energy of object free fall

  1. Mar 20, 2015 #1

    bay

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    If an object is dropped from height, h, then gravitational energy is E = mgh, but kinetic energy when object hits the ground is E=(1/2)mv^2. Conservation of energy states that E(g)=E(k). Why does kinetic energy not depend on height object was dropped?
     
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  3. Mar 20, 2015 #2

    ShayanJ

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    It does! Its equal to mgh which is a function of h!
     
  4. Mar 20, 2015 #3

    bay

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    How does the h cancel out?
     
  5. Mar 20, 2015 #4

    ShayanJ

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    It doesn't. ## E_k=\frac 1 2 m v^2 ## is the definition of kinetic energy of a particle with mass m and speed v regardless of what forces are applied to it. Any particle with mass m and speed v, has the kinetic energy ## E_k ##. Now if this particle acquired its kinetic energy by falling from a height h under constant gravitational acceleration g, then the numerical value of ## mgh ## and ## \frac 1 2 m v^2 ## will be equal which means the speed of the particle is ## v=\sqrt{2gh} ##.
     
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