The blocks shown in the figure move with a constant velocity of $10 \, m/s$ towards the right. All surfaces in contact are rough. The friction force applied by block $B$ on block $A$ is ........... $N$.

$A$ wheel with ten metallic spokes,each $0.50 \ m$ long,is rotated with a speed of $120 \ rev/min$ in a plane normal to the earth's magnetic field at the place. If the magnitude of the field is $0.4 \ G$,the induced $e.m.f.$ between the axle and the rim of the wheel is equal to:

$A$ plate of thickness $t$ made of a material of refractive index $\mu$ is placed in front of one of the slits in a double-slit experiment. What should be the minimum thickness $t$ for which the intensity at the centre of the fringe pattern is zero?

Calculate the amount of heat (in calories) required to convert $5\,g$ of ice at $0\,^{\circ}C$ to steam at $100\,^{\circ}C$.

The equation $\sqrt{3} \sin x + \cos x = 4$ has

Equilibrium constant for the reaction $H_2O_{(g)} + CO_{(g)} \rightleftharpoons H_{2(g)} + CO_{2(g)}$ is $81$. If the velocity constant of the forward reaction is $162 \ L \ mol^{-1} \ s^{-1}$,what is the velocity constant (in $L \ mol^{-1} \ s^{-1}$) for the backward reaction?