Question

An isolated system consists of two charged particles of equal mass. Initially the particles are far apart, have zero potential energy, and one of the particles has nonzero speed. If the dissipation is neglected, which of the following is true for the total energy of the system at any later time?

• A. It is negative and constant
• B. It is positive and constant
• C. It is constant, but the sign cannot be determined unless the initial velocities of both particles are known
• D. It cannot be constant because the particles exert force on each other

Answer 1

Answer: (B)

The initial potential energy of the isolated system is zero and the initial kinetic energy of the system is nonzero. No dissipative forces act within the system. Hence net energy of system is constant and equal to initial kinetic energy of the system and hence positive.