A car travelling at a speed of 54 kmph towards a wall sounds horn of frequency 400 Hz . The difference in the frequencies of two sounds, one received directly from the car and other reflected from the wall noticed by a person standing between the car and the wall is (speed of sound in air is $335 \mathrm{~m} / \mathrm{s}$ )

The speed of a transverse wave in a stretched string $A$ is $v$. Another string $B$ of same length and same radius is subjected to same tension. If the density of the material of the string $B$ is $2 \%$ more than that of $A$ then the speed of the transverse wave in string $B$ is

A heavy uniform rope is suspended vertically from a ceiling and is in equilibrium. A pulse is generated at the bottom end of the rope as shown. As the pulse travels up the rope, its acceleration at any instant is ( $g$ is acceleration due to gravity

A wave is given by the equation $y=(0.02) \sin (\pi x-8 \pi /$ then the velocity of the wave is $(y$ and $x$ are in metre and $t$ is in second)