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Homework Help: Relative momentum, Rest Energy, Kinetic energy and speed of a proton

  1. May 5, 2013 #1
    a) A relativistic proton has a momentum of 10x10^-18 kg*m/s. The rest energy of a proton is 0.150nJ. The kinetic energy of the protoon
    b) In this situation the speed of the proton is?

    2. E=MC^2
    P= MV/sqroot(1-(v^2/c^2)
    K=[MC^2/ sqroot(1-v^2/c^2)]-[mc^2]

    3. The algebra in this problem. First I found the mas of the proton by using its rest mass

    now I am trying to use the relativistic momentum to find the velocity of the object this is where my algebra is confusing. I see that v is the variable to solve but I can't get the V by itself. can anyone help me with the algebra. I do know since I will b solving for velocity in term of c then the velocity under the square root can be looked at as just v^2 instead of v^2/c^2. Even after that I tried to get rid of the square to get v in in one side and that didn't work becuase the v ended up canceling each other out any ideas on how to do this? Once I find out the velocity the Kenetic energy will be very easy to solve.
  2. jcsd
  3. May 5, 2013 #2


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    Hello, cyugsi2.

    v should not cancel out when you square the equation for p. Can you show some of your steps that led to the point where you got v to cancel?
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