The magnitude of the electrostatic force between two point charges \(Q\) and \(q\)
of the same sign is given
by \(F(x)=\frac{k Q q}{x^{2}},\) where \(x\) is the distance (measured in meters)
between the charges and \(k=9 \times 10^{9} \mathrm{N}-\mathrm{m}^{2} /
\mathrm{C}^{2}\) is a physical constant (C stands for coulomb, the unit of
charge; \(\mathrm{N}\) stands for newton, the unit of force).
a. Find the instantaneous rate of change of the force with respect to the
distance between the charges.
b. For two identical charges with \(Q=q=1 \mathrm{C},\) what is the
instantaneous rate of change of the force at a separation of \(x=0.001
\mathrm{m} ?\)
c. Does the magnitude of the instantaneous rate of change of the force
increase or decrease with the separation? Explain.