Q 12-01-125JEE MainJEE Main 2020 (8 Jan, Shift 2)Easy
A particle of mass $m$ and charge $q$ is released from rest in a uniform electric field. If there is no other force on the particle, the dependence of its speed $v$ on the distance $x$ travelled by it is correctly given by (graphs are schematic and not drawn to scale)
Answer: (B) see figure
The force $qE$ is constant, so the acceleration $a = qE/m$ is constant. Starting from rest,
$$v^2 = 2ax = \frac{2qE}{m}\,x \quad\Rightarrow\quad v \propto \sqrt{x}$$
A $v \propto \sqrt{x}$ graph starts vertically at the origin and then bends over (its slope keeps decreasing). This is graph (B).
Solution by Sreeraj P, M.Sc Physics