Three vectors are expressed as $\vec{a}=4 \hat{i}-\hat{j}, \vec{b}=-3 \hat{i}+2 \hat{j}$ and $\vec{c}=-\hat{k}$. The unit vector along the direction of sum of these vectors is

Four polaroids are placed such that the optic axis of each is inclined at an angle of $30^{\circ}$ the optic axis of the preceding one. If unpolarised light of intensity ' $\mathrm{I}_0$ ' falls on the first polaroid, the intensity of light transmitted from the fourth polaroid is $\left[\cos 30^{\circ}=\frac{\sqrt{3}}{2}\right]$

Two bodies A and B move in same straight line starting from same position. Body moves with constant velocity ' u ' and body B moves with constant acceleration ' $a$ '. When their velocities become equal, the distance between them is

The ratio of angular momentum of an electron in $\mathrm{n}^{\text {th }}$ orbit of hydrogen atom to the velocity of electron in $\mathrm{n}^{\text {th }}$ orbit is proportional to