Shown below are the positions of two small objects with identical masses and dif

Question

Shown below are the positions of two small objects with identical masses and different charges. The smaller charge is fixed in place while the +4q charge with mass m is free to move. At time t1, the charges are at rest and separated by a distance d. At a later time, t2, the charges are separated by a distance 2d. Time t1 Time t2 <----------------------------------- +4, m +q, m --------> <-------------- +4, m +q, m --------> |distance d| |distance 2d| Is the work done by the +q charge on the +4q charge during the time interval positive, negative, or zero? Explain Will the electric potential energy of the system of two charges increase, decrease, or remain the same during the time interval? Explain Will the kinetic energy of the system of two charges increase, decrease, or remain the same during the time interval? Explain Shown below is a student's drawing of the electric forces acting on object A (with charge +q and mass m) and object B (with charge +4q and mass 4m). Force on A by B Force on B by A <------------------------------------- +4q, 4m +q, m --------> There is something wrong with this diagram. Explain how to correct it.

Explanation / Answer

a)

electric potential energy of the system of two charges will decrease,

E = kq1*q2/r^2

it is proprtional to 1/r^2 hence it will decrease with increase in distance

b)

kinetic energy of the system of two charges increase since the loss in potential energy is getting converted into kinetic energy

c)

electric force on the +4q will be toward left and on +q will be towards right

but on +q an external force will also be acting in order to keep it fixed and its direction will be towards left

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