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: Electrostatics and Work

  1. Aug 15, 2012 #1
    1. The problem statement, all variables and given/known data

    I decide to use electric charges to move a 1000 kg box up a 30 degree frictionless ramp. I decide to put equal and opposite charges on the box and at the top of the 5.9 meter ramp.

    Basically there is a right triangle with a box at the bottom with +q written next to it. The hypotenuse os 5.0 meters and the base angle where the box is standing is 30 degrees. At the top, it says -q

    a) what magnitude charges do you need to keep the box from moving?

    b) what is the initial energy of the box.

    c) How much work does it take to separate the two charges from the 5.0 m apart to infinity?

    d) how much work does it take to push the piano up by hand?

    2. Relevant equations


    F=kQ1Q2/r^2 (Coulumb's Law)
    k = 9*10^9 Nm^2/C^2

    3. The attempt at a solution

    I think that you have to use cosine/sine somewhere. Also, energy is conserved so that probably has something to do with it.
    Last edited: Aug 15, 2012
  2. jcsd
  3. Aug 15, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You haven't actually indicated here what problem you are being asked to solve.

    Also, you'll have to show some sort of attempt (even a very basic start) at a solution. What have you tried so far on this problem? If you're stuck, what is it that you don't understand?
  4. Aug 15, 2012 #3
    I have edited the original thing. Sorry, I forgot about those 2 things.
  5. Aug 15, 2012 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The box is just going to slide down a frictionless ramp due to gravity, in the absence of any other forces. So, in this case, to keep the box from moving, the electric force, which is directed up the ramp, would have to cancel this gravitational force.

    You should be able to work out, from the geometry of the situation, what the component of the gravitational force parallel to the ramp is.
  6. Aug 15, 2012 #5
    Hello, but aren't we supposed to use electrostatics and find a magnitude for a charge? I really don't see how gravity will help.
  7. Aug 15, 2012 #6
    Never mind, thanks for your help. I have figured it out.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook