Two identical, small insulating balls are suspended by separate 0.36-m threads t

Question

Two identical, small insulating balls are suspended by separate 0.36-m threads that are attached to a common point on the ceiling. Each ball has a mass of 6.5 x 10-4 kg. Initially the balls are uncharged and hang straight down. They are then given identical positive charges and, as a result, spread apart with an angle of 35o between the threads. Determine (a) the charge on each ball and (b) the tension in the threads.





(a) Number Units No unitsmm/sm/s^2kgNJC
(b) Number Units No unitsmm/sm/s^2kgNJC

Explanation / Answer

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angle between the two strings is 35 degrees
so half the angle is 17.5 degrees, defined to be
T cos = mg

T = mg/cos

kqq/r2 = T sin = kq2/r2

mg tan = kq2/r2

0.36 m is the hypotenuse

so the distance between the balls is 2*hypotenuse * sin = 2*0.36*sin(17.5)

(6.5E-4)(9.8) tan(17.5) = 8.99E9(q2)/(2*0.36*sin(17.5))2

q = 1.02 E -7 C

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