What is the angle of the hanging ball in an electric field of 1.00×10^5 N/C?

AI Thread Summary
The discussion centers on calculating the angle at which a ball hangs in an electric field of 1.00×10^5 N/C. The ball is in equilibrium, meaning the tension force balances both gravity and the electric force. The initial calculations for the forces were incorrect due to a misunderstanding of the charge unit, which was in nanocoulombs instead of coulombs. After correcting the charge unit, the calculations for the forces and angle were adjusted. The final angle calculated was approximately 85.51 degrees, but the accuracy of this result was questioned due to the initial error.
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Homework Statement


http://session.masteringphysics.com/problemAsset/1001949/13/knight_Figure_25_69.jpg
An electric field 1.00×10^5 N/C causes the ball in the figure to hang at an angle. What is theta?



Homework Equations


E = F/q
F = mg

The Attempt at a Solution


The ball isn't accellerating, so it is in equilibrium. Sum of all forces is 0, so the tension force balences gravity + electric field.

E = F/q
F = Eq
F = 100000*(25*0.000001)
Fx = 2.5

F = mg
F = (0.002)(9.81)
Fy = 0.1962

Ft = Sqrt(Fx^2 + Fy^2)
Ft = 2.5076870697916038024546202698347

tan(theta) = Opp/Adj
tan(theta) = Fx/Fy
theta = arctan(2.5 / 0.1962)
theta = 85.5126 degrees

This answer is wrong.
Where is my mistake?
 
Last edited:
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You have not given the unit for the electric field, but I'm assuming it's in SI.

> F = 100000*(25*0.000001)

The charge is in nC...
 
Ah. Yeah, when I copied it over from the online problem, it didn't go.
E = 1x10^5 N/C
So I figured I'd convert q into the unit C, therefore get F in the unit N.
 
Did you get the right answer?
 
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