1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Kinetic energy alpha particle

  1. Dec 25, 2013 #1
    1. The problem statement, all variables and given/known data

    could you help me for the question b?

    2. Relevant equations
    E = mc^2

    3. The attempt at a solution

    the mass of the alpha particle is 0.66466 x 10^-26 kg >> 4.022 u

    put it into the equation, so
    E = 4.022 x c x c = 3.615 x 10^17 eV >> 0.0579 joule

    my answer is that, but my teacher answer is 1.89x10^-13 joule..

    which one is true? can you show me where's my wrong?

    Attached Files:

    Last edited: Dec 25, 2013
  2. jcsd
  3. Dec 25, 2013 #2


    User Avatar
    Homework Helper

    Merry Xmas.

    What you're calculating is the energy due to the (rest) mass of the alpha particle. That's not kinetic energy.

    The alpha particle's total energy comprises energy due to its (rest) mass plus its kinetic energy. You need to determine the latter.

    You can just work with mass, because mass and energy are basically equivalent (or proportional, depending on choice of units). Calculate the total mass of on the left hand side. Calculate the total mass on the right hand side. You may ignore the photon because at the minimum KE of the alpha particle, the photon will have no energy. Can you now figure out the "extra" mass on the LHS? Convert that to energy.
  4. Dec 25, 2013 #3
    merry christmas too ;)

    thankyou :D i understand it now!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted