As shown in the figure above two small (negligible size) copper balls each havin
ID: 1600637 • Letter: A
Question
As shown in the figure above two small (negligible size) copper balls each having the same charge and mass 7 g are hanging on the ends of a 50 cm long string. The strings are tied together to the ceiling as shown in the figure. When they are in equilibrium the strings make an angle 60 degree with each another (a) What is the charge on each sphere ? (b) What will be the sign of each charge ? (c) Will anything change in this problem if the balls have the same mass but each have a diameter of 20 cm. ?Explanation / Answer
m = 7 g , L = 50 cm
cos(30) = d/L
cos(30) = d/0.5
d = 0.433 m
r = 2d = 2*0.433
r = 0.866 m
net force along vertical direction
Tsin(60) = mg
Tsin(60) = 0.007*9.8
T = 0.079 N
net force along horizotnal direction
Tcos(60) = F
F = kq^2/r^2
0.079*cos(60) = 9*10^9*q^2/0.866^2
q = 1.814*10^-6 C
(b) Both have positive charge.
(c) yes, charge also increased. becuse distance between center of two sphere is increased
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