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Homework Statement
Your physics assignment is to figure out a way to use electricity to launch a small 6.0-cm-long plastic drink stirrer. You decide that you'll charge the little plastic rod by rubbing it with fur, then hold it near a long, charged wire. When you let go, the electric force of the wire on the plastic rod will shoot it away. Suppose you can charge the plastic stirrer to 18.0 nC and that the linear charge density of the long wire is 1.0 *10^ - 7C/m} .
http://session.masteringphysics.com/problemAsset/1002026/9/knight_Figure_26_69.jpg
What is the electric force on the plastic stirrer if the end closest to the wire is 2.0 cm away?
Homework Equations
E (of long wire) = (k2|lamda|)/r
F= qE
E(rod) = (k|Q|)/r(sqrt(r^2 + (L/2)^2))
Q = q = 18nC
The Attempt at a Solution
i know i have to find r the distance from the wire to a point of the rod but i can't figure out how
this is wat i tried:
(k|Q|)/r(sqrt(r^2 + (L/2)^2))=(k2|lamda|)/r
isolate r
then, r = sqrt((Q/2lamda)^2 - (L/2)^2)
r = 0.04
i think my understanding is wrong ...i don't know if the charged stirrer is producing an electric field
some how i am suppose to fine the E of the wire
and use it to find force where
Fnet on the stirrer = F (of wire = electrostatic) + F (of repulsion since both the wire and the stirrer are the same charge) = ma
i just can't figure out how to get to the force part