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Homework Help: Energy and mechanics question

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data
    http://img120.imageshack.us/img120/3743/physicsquestionnb9.jpg [Broken]
    http://g.imageshack.us/img120/physicsquestionnb9.jpg/1/ [Broken]

    3. The attempt at a solution

    I'm trying this problem and I'm really not sure if my answers are correct at all.

    For part a) I get the kinetic energy = Pt (since it is the electrical energy)
    I make 0.5m.v^2=Pt and make v the subject, leaving [itex]v=\sqrt \frac{2pt}{m}[/itex]

    Now I hope what I've done so far is okay. For part b to find the acceleration I differentiated the equation I derived above. To do this I wrote the equation as
    [itex]v=(\sqrt \frac{2p}{m})t^\frac{1}{2}[/itex]

    and so

    [itex]dv/dt = \frac{1}{2}(\sqrt \frac{2p}{m})t^\frac{-1}{2}[/itex]

    While for the distance, by integration, I got

    [itex]s= \frac{2}{3}(\sqrt \frac{2p}{m})t^\frac{3}{2}[/itex]

    Im not very confident in my maths so I'd appreciated it if somebody could check whether I got the right results.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Nov 3, 2008 #2
    As long as your first assumption is correct, that power times t is equal to the kinetic energy, you did the integration and the derivations correctly.
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