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Homework Help: First derivative of KE

  1. Sep 19, 2009 #1
    I had a question on the first derivative of Kinetic Energy.....This a problem from the FE exam....

    Now the solution is = mva.....which turns out to be power.....im just trying to understand how they came up with that....

    so KE = 1/2 mv^2

    im asuming they are using the general power rule so v^2 would be 2v dv/dt where dv/dt is acceleration......

    the m is where im confused....the derivative of m would just be 1....but why not dm/dt as well...obviously it wouldnt make sense because the mass wouldnt change with time....but i guess im rusty on the power rule....
  2. jcsd
  3. Sep 19, 2009 #2


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    m is a constant, v is the only thing changing with time, that's why you differentiate the v2 with respect to t
  4. Sep 19, 2009 #3
    perfect!....that makes sense....I thought it was something to do with mass not changing....but i forgot i was taking the derivative with respect ot time...

    thank you
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