A source of unknown frequency gives 4 beats/s when sounded with a source of known frquency 250 Hz. The second harmonic of the source of unknown frequency gives five beats per second, when sounded with a source of frequency 513 Hz. The unknown frequency is

If we study the vibration of a pipe open at both ends. then the following statement is not true.

A wave travelling in the + ve x-direction having displacement along y-direction as 1 m, wavelength 2$$\pi $$ m and frequency of $${1 \over \pi }$$ Hz is represented by

A train moving at a speed of 220 m s^$$-$$1 towards a stationary object, emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is
(Speed of sound in air is 330 m s^$$-$$1)