Three identical cars $A, B$ and $C$ are moving at the same speed on three bridges. The car $A$ goes on a plane bridge, $B$ on a bridge convex upward and $C$ goes on a bridge concave upward. Let $F_{\mathrm{A}}, F_{\mathrm{B}}$ and $F_{\mathrm{C}}$ be the normal forces exerted by the cars on the bridges when they are at the middle of bridges.

An object follows a curved path. The following quantities may remain constant during the motion. 

Assume that the Earth goes around the Sun in a circular orbit with a constant speed of $30 \mathrm{km} {\mathrm{s}}^{-1}$.

The position vector of a particle in a circular motion about the origin sweeps out equal area in equal time. Its