The figure shows wave fronts in still water,moving in the direction of the arrow towards the interface $PQ$ between a shallow region and a deep (denser) region. Which of the lines shown may represent one of the wave fronts in the deep region?

If a body is projected with an angle $\theta$ to the horizontal,then

$A$ car is moving with a speed of $72 ~km/h$ towards a hill. The car blows its horn at a distance of $1800 ~m$ from the hill. If the echo is heard after $10 ~s$,what is the speed of sound in $m/s$?

If $b$ and $c$ are the lengths of the segments of any focal chord of a parabola $y^2 = 4ax$,then the length of the semi-latus rectum is:

When a metallic surface is illuminated with radiation of wavelength $\lambda$,the stopping potential is $V$. If the same surface is illuminated with radiation of wavelength $2\lambda$,the stopping potential is $\frac{V}{4}$. The threshold wavelength for the metallic surface is:

$0.066 \ g$ of metal was deposited when a current of $2 \ A$ is passed through a metal ion solution for $100 \ s$. What is the electrochemical equivalent (in $g \ C^{-1}$) of the metal?