Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating charge dissipation given two hanging masses

  1. Jun 27, 2011 #1
    1. The problem statement, all variables and given/known data

    Two hanging masses have an identical charge and create an angle theta from the vertical. If they start losing their charge and have an instantaneous velocity of XX m/s(given), find the rate in which they are losing the charge.

    2. Relevant equations

    Coulumbs Law

    3. The attempt at a solution

    The first part of the question was to find theta, which I did. I now have no idea how to handle it from here. The only thing I came up with is-

    dq/dt = dx/dt * dq/dx

    Where dq/dt is what I am trying to find, dx/dt is the given velocity and dq/dx would be the change in charge in terms of the distance from the vertical. I'm not sure how to find that.

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

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 28, 2011 #2


    User Avatar
    Homework Helper

    I don't think dx/dt is the instantaneous velocity, because the velocity should also include dy/dt. Instead, the charges are tracing out a circle, so their velocity should be L*d(theta)/dt, where L is the length of the string.

    Since you already have an equation for theta, presumably in terms of q, why not derive both sides with respect to time? On the left side, you'll get d(theta)/dt. On the right side, you'll get a factor of dq/dt, which is the factor you're trying to solve for.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook