physics
posted by H .
A small sperical insulator of mass 8.00X10^2 kg and charge +0.600 mC is hung by a thin wire of negligible mass. A charge of 0.900 mC is held 0.150 m away from the spere and directly to the right of it, so the wire makes an angle [theta] with the vertical. Find (a) the angle [theta] and (b) the tension in the wire.

Let T be the tension in the wire.
A vertical force balance of the insulator says:
T sin theta = M g
A horizontal force balance says :
T cos theta = k Q1*Q2/R^2
which is Coulomb's law. k is the Coulomb constant and Q1 and Q2 are the two charges.
Solve the two equations in the two unknowns, theta and T.
Hint: divide one equation by the other to get tan theta and eliminiate T.