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Homework Help: [Physical Science:] Finding Kinetic Energy

  1. Feb 13, 2005 #1
    Two homework problems I don't understand. :(

    9. An alpha particle travels at 1.6 x 10^7 m/s. The kinetic energy of the particle is 6.0 x 10^-13 J. What is the mass of the alpha particle?

    I think scientific notation is supposed to be used, so "1.6 x 10^7" is 16,000,000 and "6.0 x 10^-13" is .0000000000006, but I still don't know what to do with the numbers.

    10. An electron with a mass of 9.0 x 10^-31 kg moves through a vacuum with a speed of 2.5 x 10^8 m/s. Find the electron's kinetic energy.

    Again, I'm guessing "9.0 x 10^-31" is .0000000000000000000000000000009 and "2.5 x 10^8" is 250000000, so does that make the answer 2.8125 x 10^-14
  2. jcsd
  3. Feb 13, 2005 #2
    Kinetic Energy is found by the equation

    K.E. = .5 *m* v^2

    where m = mass and v = velocity
  4. Feb 13, 2005 #3


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    You may wanna use the relativistic formula for the second case,though,it's roughly 83% of the speed of light...


    P.S.And yes,please use scientific notation...Nobody will be willing to count the zeros...
  5. Feb 13, 2005 #4
    I'm given the kinetic energy - how do I find the mass?

    Dexter, I'm sorry..I didn't understand anything that you said. I don't think I'm familiar with the relativistic formula. I'm guessing what I did was wrong, then? :P
  6. Feb 13, 2005 #5


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    Okay,no problem,then don't use it.Use the classical one.Extract mass,knowing the KE and velociy.A mere division...

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