$21\mathrm{.}79*$ CALC Positive charge $Q$ is distributed uniformly along the $x-$axis from $x=0$ to $x=a.$ A positive point charge $q$ is located on the positive $x-$axis at $x=a+r,$ a distance $r$ to the right of the end of $Q($Fig$.$ P$21\mathrm{.}79).($a$)$ Calculate the $x-$ and $y-$components of the electric field produced by the charge distribution $Q$ at points on the positive $x-$axis where $x>a.($b$)$ Calculate the force $($magnitude and direction$)$ that the charge distribution $Q$ exerts on $q.($c$)$ Show that if $ra,$ the magnitude of the force in part $($b$)$ is approximately $Q\frac{q}{4}lo{n}_0{r}^2.$ Explain why this result is obtained.