The displacement $x$ of a particle varies with time $t$ as $x = a e^{-\alpha t} + b e^{\beta t}$,where $a, b, \alpha$,and $\beta$ are positive constants. The velocity of the particle will:

Two spherical conductors $A$ and $B$ of radii $1 \ mm$ and $2 \ mm$ are separated by a distance of $5 \ cm$ and are uniformly charged. If the spheres are connected by a conducting wire,then in the equilibrium condition,the ratio of the magnitude of the electric fields at the surfaces of spheres $A$ and $B$ is-

The standard deviation of the numbers $22, 26, 28, 20, 24, 30$ is

From which of the following minerals is $Ra$ (Radium) obtained?

If $y=\tan ^{-1}\left(\frac{\sqrt{1+a^2 x^2}-1}{a x}\right)$,then $\left(1+a^2 x^2\right) y^{\prime \prime}+2 a^2 x y^{\prime}$ is equal to

The position vector of a point lying on the line joining the points whose position vectors are $\hat{i}+\hat{j}-\hat{k}$ and $\hat{i}-\hat{j}+\hat{k}$ is: