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

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Homework Help Overview

The problem involves determining the angle at which a ball hangs in an electric field of 1.00×10^5 N/C. The context is centered around the forces acting on the ball, including gravitational and electric forces, and the conditions for equilibrium.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply equilibrium conditions to find the angle theta, but questions arise regarding the unit of charge used in calculations. Some participants suggest clarifying the unit of the electric field and the charge to ensure correct force calculations.

Discussion Status

The discussion is ongoing, with participants exploring the implications of unit conversions and their effects on the calculations. There is no explicit consensus yet, as the original poster acknowledges a potential mistake in their approach.

Contextual Notes

There is a noted lack of clarity regarding the unit of charge, which may affect the calculations. The original poster's reference to the problem source indicates that there may be additional context or constraints not fully detailed in the posts.

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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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