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: Finding the kinetic energy of an electron

  1. Apr 18, 2012 #1
    1. The problem statement, all variables and given/known data

    An electron's position is given by r(t)=r(0)+c1*t, θ(t)=θ(0)+c2*t, where r(0), c1, θ(0), and c2 are known constants. What is the kinetic energy of the electron? (mass=m)

    2. Relevant equations


    3. The attempt at a solution

    plugging in m for mass, r(0)+c1*t for radius, and c2 for ω

    This isn't the correct answer, so I'm fairly certain I've messed up on my "r" value somehow.

    It's supposed to equal (1/2)(m)(c12+r2c22)

    Where am I going wrong?
  2. jcsd
  3. Apr 18, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    hi texan14! :smile:
    what on earth are you doing? :confused:

    that's for a rigid body with angular velocity ω

    this is a spiral … you have no idea what ω(t) is, it certainly isn't θ'

    start again, and just use v = (r',rθ') :smile:

    (you do know how to prove that, don't you? … if you don't, then look it up)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook