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Homework Help: Mass with a Charge in side an electric field

  1. Nov 4, 2008 #1
    1. The problem statement, all variables and given/known data
    A block having mass m and charge +Q is connected to an insulating
    spring having force constant k. The block lies on a frictionless, insulating horizontal track, and the system is immersed in a uniform electric field of magnitude E
    The block is released from rest at a moment when the spring is unstretched (that is, when x = 0).
    (a) By what maximum amount does the spring expand?
    (b) What is the equilibrium position of the block?
    (c) Show that the block’s motion is simple harmonic and determine its period.
    (d) What if? Repeat part a, assuming now that there is friction between the block and track. Take mew sub k as the relevant coe¢ cient of kinetic friction.

    2. Relevant equations

    3. The attempt at a solution

    Not sure how to tackle this problem.
  2. jcsd
  3. Nov 4, 2008 #2


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    Homework Helper
    Gold Member

    Since your not told anything about whether the block is an insulator or conductor or the dimensions of the block or how the charge distributes itself through the block; the best you are going to be able to do is to assume it can be effectively treated as a point charge with mass [itex]m[/itex] and charge [itex]Q[/itex]...What is the electric force on such a charge when it is put in an electric field [itex]\vec{E}\hat{x}[/itex]? (I assume that the field is in the x-direction here?)....What other forces are being exerted on the charge?
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