# Mass with a Charge in side an electric field

1. Nov 4, 2008

### shinobi12

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. Nov 4, 2008

### gabbagabbahey

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 $m$ and charge $Q$...What is the electric force on such a charge when it is put in an electric field $\vec{E}\hat{x}$? (I assume that the field is in the x-direction here?)....What other forces are being exerted on the charge?