A source of sound emitting a note of frequency $90 \mathrm{Hz}$ moves towards an observer with speed equal to ${\left(\frac{1}{10}\right)}^{\text{th }}$ of velocity of sound. The frequency of the note heard by the observer will be,

A train has just completed a U-curve in a track which is a semi-circle. The engine is at the forward end of the semi circular part of the track while the last carriage is at the rear end of the semicircular track. The driver blows a whistle of frequency $200 \mathrm{Hz}$. The velocity of sound is $340 \mathrm{m} {\mathrm{s}}^{-1}$. Then, the apparent frequency as observed by a passenger in the middle of a train when the speed of the train is $30 \mathrm{m} {\mathrm{s}}^{-1}$ is,

Assertion: On reflection from a rigid boundary (denser medium), there is a complete reversal of phase.

Reason: This is because, on reflection at a denser medium, both the particle velocity and wave velocity are reversed in sign.

A sound source emits sound waves in a uniform medium. If energy density is $E$ and maximum speed of the particles of the medium is $v_{\text{max}}$, the plot between $E$ and $v_{\max }$ is best represented by,

The well known example of longitudinal waves is,

When a tuning fork produces sound waves in air, which one of the following is same in the material of tuning fork as well as in air?

The wave described by, $y=0.25\sin (10\pi x-2\pi t)$ where, $x$ and $y$ are in $\mathrm{meters}$ and $t$ in $\sec$, is a wave travelling along the,

Given that $y=A\sin \left[\left(\frac{2\pi }{\lambda }(ct-x)\right)\right],$ where $y$ and $x$ are measured in metres. Which of the following statements is true?

The equation of a plane progressive wave is given by $y=3$sin $\pi \left(\frac{t}{0.02}-\frac{x}{20}\right)$ . The frequency of the wave is