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Thu 24 May, 2007 08:18 am
Two identical balls each having a charge of 2*10^-7C
and mass=100g are suspended
from a common point by two insulating strings each 50cm long.The balls are held at a separation 5cm apart and released.Find tension in the string.
Draw yourself a diagram. Find all the relevant angles as you are given two sides of a triangle, 50cm & 50cm. Find the weight of one ball W = mg, using kilograms ofcourse.
Now, the system is static, so the forces are in equilibrium; so consider the forces acting on one ball: the tension in the string, the weight of the ball downwards and the electro-static force horizontally. These three forces should form a right-angled triangle (they are in equilibrium). You will know two forces, the weight, and the electro-static force, which you will easily calculate. Since you have a right-angled triangle, and two sides (the two forces), you can calculate the tension, which is the last, missing force.
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