Three blocks,$A, B$ and $C,$ of masses $4\,kg, 2\,kg$ and $1\,kg$ respectively,are in contact on a frictionless surface,as shown. If a force of $14\,N$ is applied on the $4\,kg$ block,then the contact force between $A$ and $B$ is ....... $N$.

The position of a projectile launched from the origin at $t=0$ is given by $\vec{r}=(40 \hat{i}+50 \hat{j}) \text{ m}$ at $t=2 \text{ s}$. If the projectile was launched at an angle $\theta$ from the horizontal,then $\theta$ is (take $g = 10 \text{ m/s}^2$)

$A$ parallel plate capacitor with oil (dielectric constant $K = 2$) between the plates has capacitance $C$. If the oil is removed,the capacitance of the capacitor becomes:

$A$ cell is connected between the points $A$ and $C$ of a circular conductor $ABCD$ of centre $O$ with angle $AOC = 60^{\circ}$. If $B_1$ and $B_2$ are the magnitudes of the magnetic fields at $O$ due to the currents in $ABC$ and $ADC$ respectively,the ratio $\frac{B_1}{B_2}$ is

Total internal reflection of light is possible when light enters from

Two point charges $+9e$ and $+e$ are placed at a distance of $16\, cm$ apart. Where should a third charge $q$ be placed between them so that it remains in equilibrium?