57. On a vertical plane, a charge with a surface density of 4 л 10−5 Kl / m2 is distributed. A thread is attached to the plane, at the end of which there is a charged ball weighing 10–3 kg. When the system is in equilibrium, the thread forms an angle of 13 ° with the plane. Determine the charge of the ball.

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)