Finding the E-field of a mass hanging from a string

AI Thread Summary
The discussion centers on calculating the electric field (E) for a ball of mass 0.480 g and charge 32.7 µC suspended at a 15° angle. The equations of motion are established, with the balance of forces in the x and y directions leading to the relationship between tension, gravitational force, and electric force. The user attempts to calculate E using the formula E = (Tan(15°) * m * g) / q, resulting in a value of approximately 3.9 x 10^4 N/C. A note is made regarding the mass units, indicating a potential source of error. The thread was also moved to the appropriate homework forum for better visibility.
aximwolf
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9. [1pt]
prob04_ball_in_field.gif


As shown in the figure above, a ball of mass 0.480 g and positive charge q =32.7microC 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?

Fx= Fe - Tsin(theta)= 0
Fy= Tcos(theta) = 0

Tsin(theta)/Tcos(theta) = Fe\mg

Than E= Fe/q

So Tan(theta)mg = Fe/q = E

I got (Tan(15)*.480*9.8)/32.7e-6= 3.9 e 4
Where did I go wrong?
 
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Note the units in which the mass was specified.

EDIT: Note also that since this is a homework problem, it should have been posted in one of the homework forums, in particular the Introductory Physics Forum.

EDIT by mentor: this thread has been moved to the appropriate location.
 
Last edited by a moderator:
Its right! Thank you for responding so fast!
 

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