Problem 4:The work done by an external agent in moving a positively charged object that starts from rest at infinity and ends at rest at the point P midway between two charges of magnitude +0 and -20, starts at infinity ● 9>0 ends at midpoint p ● -29 1.is positive. 2.is negative 3.is zero 4.cannot be determined-not enough info is given. Answer 2 negative. The work done by the external agent in moving the positive charge g from infinity to the point P is equal to the negative of the work done by the electrostatic force.Each charged object is the same distance d from the point P.The work done by the electrostatic force is equal to the potential energy difference between infinity and the point P,which is given by A=qar=g号629}0 44 Problem 4: The work done by an external agent in moving a positively charged object that starts from rest at infinity and ends at rest at the point P midway between two charges of magnitude +Q and !2Q , 1. is positive. 2. is negative. 3. is zero. 4. cannot be determined – not enough info is given. Answer 2 negative. The work done by the external agent in moving the positive charge q from infinity to the point P is equal to the negative of the work done by the electrostatic force. Each charged object is the same distance d from the point P. The work done by the electrostatic force is equal to the potential energy difference between infinity and the point P, which is given by !U = q!V = q ke Q d " ke 2Q d # $ % & ' ( < 0