Two identical small insulating balls are suspended by separate 0.291m threads that are attached to a common point on the ceiling. Each ball has a mass of 7.90×10-4kg. 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 35.0o between the threads. Determine the charge on each ball.
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r = distance between the two balls = 2 BC = 2 (0.291) Sin17.5 = 0.175 m
q = charge on each ball
m = mass of the ball = 7.9 x 10-4 kg
T = tension force in the string
using equilibrium of force in vertical direction
T Cos17.5 = mg
T = mg/Cos17.5 eq-1
using equilibrium of force in horizontal direction
T sin17.5 = F
T Sin17.5 = k q2/r2
using eq-1
(mg/Cos17.5) Sin17.5 = k q2/r2
mg tan17.5 = k q2/r2
(7.9 x 10-4) (9.8) tan17.5 = (9 x 109) q2/(0.175)2
q = 9.11 x 10-8 C
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