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Homework Help: Help relativity exam in in 5 hours

  1. Mar 7, 2005 #1
    urgent help relativity exam in in 5 hours

    an electrion with mass 9.11e031 kg has momentum 4e-22. what is its kinetic energy

    the answer is 6.3e-14 J but i have no idea how to get here

    relativity kinetic energy = (y-1)mc^2 where y = 1/(square root of 1-(v^2/c^2)

    momentum = ymu

    thats as far as i can get , how the hell can u solve this type of problem if they dont give u the velocity of the electron?
     
    Last edited: Mar 7, 2005
  2. jcsd
  3. Mar 7, 2005 #2
    We have a soln .
    We have K.E = (P^2)/2m;
    where KE is kinetic energy,P is momentum

    So solving eqn u can get the answer
     
  4. Mar 7, 2005 #3
    i got 8.78e-14

    when plugging into that equation?
     
  5. Mar 7, 2005 #4

    dextercioby

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    Use this
    [tex]E^{2}=m_{0}^{2}c^{4}+p^{2}c^{2} [/tex] to find the total energy and then from that simply subtract the rest energy...

    Daniel.
     
    Last edited: Mar 7, 2005
  6. Mar 7, 2005 #5
    thank u!! i was stuck on that problem forever
     
  7. Mar 7, 2005 #6

    dextercioby

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    U'd better memorize that formula.It's the most important in the Special Relativity,at least,not in Minkowski space.

    Daniel.
     
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