A pith ball of mass 1.0 x 10-5 kg with a positive charge of 4.0 x 10-7 C is slowly pulled by a string a distance of 50 cm through a potential difference of 8.0 x 10-2 V. It is then released from rest and “falls” back to its original position. Calculate: (a) the work done by the string in moving the pith ball. (b) the average force required to do this work. (c) the kinetic energy with which the pith ball reaches its original position. (d) its speed just as it reaches its original position. (3 marks)

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