1. Not finding help here? Sign up for a free 30min 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!

Simple Kinetic energy problem

  1. Oct 27, 2007 #1
    [SOLVED] Simple Kinetic energy problem

    1. The problem statement, all variables and given/known data

    A proton travelling at 23 degrees with respect to the direction of a magnetic field of strength 2.6mT experiences a magnetic force of 6.5*10^-17 N. Calculate a) the proton's speed and b) its kinetic energy in electron-volts

    2. Relevant equations

    For part a) I simply used F=qvbsin(theta), I got the correct answer of 400,000m/s
    For part b) I used K = 0.5*m*v^2

    3. The attempt at a solution

    For part b) I plugged in the value of 9.1*10^-31 for m and the value of v I found above(400,000m/s). I return 7.28*10^-20 (assume this in in J?). Upon conversion to eV I find a measly 0.45eV. (The answer is 835ev!)
     
  2. jcsd
  3. Oct 27, 2007 #2
    It's a proton, not an electron.
     
  4. Oct 27, 2007 #3
    I had a feeling this might be it. I assumed charge of proton and electron is the same, got the right answer, so then I proceeded to assume mass was the same too.

    Now if I plug in 1.67262158 × 10-27 instead, I get 835eV!

    Thanks
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?