imzkris
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Homework Statement
When an electrically charged object (a proton, an electron, a balloon after you’ve rubbed it
on your hair) is placed in an electric field, E , an electric force proportional to this field acts
on the object. Specifically,
F = qE
where q is the charge on the object and is in units called Coulombs (C).
The figure shows a pendulum, the bob of which is charged. The ambient electric field is
uniform, directed toward the right, and has a magnitude of 2 × 10^5 N/C. The pendulum
hangs at an angle of 20 degrees as a result of the forces acting on it. What is the charge on the bob of the pendulum? The string can be considered of negligible mass and uncharged.
So:
(theta) = 20 degrees
E = 2 x 10^5 N/C
m = 5.0g (or 0.005kg)
a(g) (acceleration due to gravity) = -9.8m/s
F(e) (force of electric... thing) = ?
T(xy) (x and y component of tension in rope) = ?
F(net) (net force) = 0
Homework Equations
F = ma
F = qE
probably like four I can't remember
The Attempt at a Solution
I know that F(net) is zero, 'cause it's a static system. So:
F(net) = T(xy) - F(e) - F(g) = 0
The force of gravity is 0.049N (0.005kg*9.8m/s^2).
But I have no idea how to find the tension in the rope. If I could get it, the only thing left would be to solve for F(e) using the net force equation, and then rearrange the F(e) = qE equation to solve for q, but that's the easy part.
The second long-distance force is throwing me off. Also, I forget all of high school trig (it's been like, four years) and even then I'm not sure how I would apply it. cos(theta)*T(xy) = T(y), sin(theta)*T(xy) = T(x) (which, I'm kind of grabbing at straws here, so I give myself a 50/50 chance on being right). So what - I can't see a way for me to get or apply either of those. I'm stuck. :<
Thanks for reading.
EDIT: Is the magnitude of T(x) just the same as F(g)? If it is I'm going to be mad, 'cause this took way too long. :'(
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