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Coulomb's law and mechanics

  1. Apr 3, 2005 #1
    Hey....i need help....

    "One practical arrangement for verifying Coulomb's law is to use a lightweight, negatively charged, freely-suspended ball. it is repelled by the negative charge on a larger sphere that is held near it, on an insulated support. the small angle of deflection, x is then measured.

    The weight of the ball is W. show that the force of repulsion F on the suspended ball is given by:

    F = W tan x"

    I've drawn a free body force diagram, but i still cant work it out..
    help pleaseee
  2. jcsd
  3. Apr 3, 2005 #2

    Doc Al

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    Staff: Mentor

    Start by identifying the forces acting on the suspended ball. (Hint: Three forces act on that ball.) Then apply the conditions for equilibrium: the sum of the forces must be zero. (Hint: Consider vertical and horizontal components separately.)
  4. Apr 3, 2005 #3
    Ok I've got to the point where I've found that the components of N (the normal reaction force) are:

    N sin x


    N cos x

    I don't study maths so could you please give me hints as to how I turn the above into F = W tan x???
  5. Apr 3, 2005 #4

    Doc Al

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    Staff: Mentor

    I don't know what you mean by the "normal force" in this problem. Answer the questions I asked in my last post: What are the forces acting on the ball?
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