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

As shown in the figure above, a ball of mass 0.720 g and positive charge q =39.4microC is suspended on a string of negligible mass in a uniform electric field. We observe that the ball hangs at an angle of theta=15.0o from the vertical. What is the magnitude of the electric field?

(The figure shows the ball hanging 15 degrees to the left of the y-axis, and the electric field points to the left)

2. Relevant equations

F = ma

E = F/q

Sum of forces = 0

Sum of forces = tension + e-field - weight = 0

3. The attempt at a solution

I drew a free-body diagram, and found the forces due to the tension and weight to be

F = mg*cos(15) or F = 6.816

Then I used E = F/q, to get 1.73*10^5 N/C

I think I'm missing a step? Or calculating the force incorrectly? Thank you!

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# Homework Help: Finding an electric field magnitude with tension and weight of hanging ball

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