(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A dust cobweb is drawn from an initial vertical position toward a nearby wall by an electrostatic force. Assume the cobweb to be like a single dust ball of mass 2.0 x 10^{-7}g suspended on a massless string of length 0.42 m connected a horizontal distance of 0.35 m from the wall, as shown below. The tethered dust ball is drawn to the wall by another similar dust ball of opposite charge, -q = -3.0 x 10^{-6}C, as shown.

a) Draw a free-body diagram for the tethered dust ball in its final resting position.

b) Transfer the force information from the free-body diagram to a triangle. (I think they mean a component triangle)

c) What is the final charge on the cobweb?

2. Relevant equations

F_{e}= [tex]\frac{Kq_{1}q_{2}}{d^{2}}[/tex]

where F_{e}is the electric force between two objects

K is Coulomb's constant (9.0 x 10^{9}Nm^{2}/C^{2})

q_{1}is object 1's electric charge

q_{2}is object 2's electric charge

d is the distance between centers of charged objects

3. The attempt at a solution

a) just draw the Normal Force, Force of Gravity, and the Electric force?

b)unsure, but i could figure this out alone

c) Would I just solve for the distance between the two dust balls and then sub that into the equation above, using +q for q_{1}and -q for q_{2}and 9.0 x 10^{9}for K?

edit: bah, nevermind that failed. need help for c)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Coulomb's Law of a cobweb

**Physics Forums | Science Articles, Homework Help, Discussion**