coulomb's law

[tandoorichicken]

Two equally charged insulating balls each weigh 0.1 g and hang from a common point by identical threads 30 cm long. The balls repel each other so that the separation between their centers is 8.0 cm. What is the magnitude of the charge on each ball?

[Moose352]

Find the angle that the string makes with the horizontal. Then you know that cos(theta)*Ft (tension in string) will equal the force exerted on balls by each other. You also know that sin(theta)*Ft will equal the weight of the ball.

[tandoorichicken]

There are two strings attached to the same point. At the end of each string is a charged ball. The balls repel each other. This forms a triangle with two legs 30 cm and the horizontal leg 8 cm long. I am a little confused about your explanation, because it makes it seem like there is only one string.

[Moose352]

Note the symmetry of the problem.