Question

A spring of spring constant $K$ is fixed at one end has a small block of mass $m$ and charge $q$ is attached at the other end. The block rests over a smooth horizontal surface. A uniform and constant magnetic field $B$ exists normal to that plane of paper as shown in figure. An electric field $\overrightarrow{E}=E_0\hat{i}$ ($E_0$ is a positive constant) is switched on at $t=0sec$. The block moves on horizontal surface without ever lifting off the surface. Then the normal reaction acting on the block is

• A. Maximum at extreme position and minimum at mean position
• B. Maximum at mean position and minimum at extreme position
• C. is uniform throughout the motion
• D. is both maximum and minimum at mean position

Answer 1

The correct option is A Maximum at extreme position and minimum at mean position

$N=mg-F_{\overrightarrow{B}}=mg-\left(qVB\right)$

At extreme position- V is minimum $\Rightarrow$ N is maximum

At mean position -V is maximum $\Rightarrow$ N is minimum.