In Millikan's experiment,an oil drop having charge $q$ becomes stationary upon applying a potential difference $V$ between two plates separated by a distance $d$. The weight of the drop is:

The angle between the lines whose direction cosines satisfy the equations $l+m+n=0$ and $l^2+m^2-n^2=0$ is

The maximum value of $xy$ when $x + 2y = 8$ is

Thermite is a mixture of $X$ parts of ferric oxide and $Y$ parts of aluminium powder. What are $X$ and $Y$ respectively?

The ratio of the radii of nuclei $_{13}Al^{27}$ and $_{52}X^A$ is $3:5$. The number of neutrons in the nucleus of $X$ will be:

Two persons $A$ and $B$ are located in the $X-Y$ plane at the points $(0,0)$ and $(0,10)$ respectively. (The distances are measured in $MKS$ units). At time $t=0$,they start moving simultaneously with velocities $\overrightarrow{v}_A = 2\hat{j} \text{ m/s}$ and $\overrightarrow{v}_B = 2\hat{i} \text{ m/s}$ respectively. The time after which $A$ and $B$ are at their closest distance is