KVPY SA Exam 19-Nov-2017 Question Paper

Four identical pendulums are made by made by attaching a small ball of mass 100 g on a 20 cm long thread and suspended from the same point. Now each ball is given charge Q so that balls move away from each other with each thread making an angle of 45° from the vertical. The value of Q is close to ($\frac{1}{4\mathit{\pi }{\in }_0}=9\times {10}^9$in SI units)