A thin dielectric rod is uniformly charged with linear charge sensity $\lambda$. A point $A$ is located at the distance $h$ from the rod and is equidistant from it ends. The rod substands an angle of $2 \varphi$ from point $A$ (see fig.).
1
Determine the electric field in the point $A$.
A thin dielectric square plate of side length $L$ is uniformly charged with a surface charge density $\sigma > 0$. A smooth, charged puck with a charge of $q<0$ and a mass of $m$ is held at point $A$. A distance between $A$ and the center $O$ is $r\ll L$ and the segment $OA$ forms an angle $\alpha = 60^\circ$ with a side of square. The puck is released without initial speed.
2.1
Determine the magnitude and the direction of the acceleration of the puck immdiatly after the releasing.
2.2
Determine the time $t$ when the distance between the puck and the origin will be minimal for the first time.
