Test Preparation on Wave and Sound-IV-Physics Test Series For NEET 2020

A motor cycle starts from rest and accelerates along a
straight path at 2 2m/ s . At the starting point of the motor
cycle there is a stationary electric siren. How far has the
motor cycle gone when the driver hears the frequency of
the siren at 94% of its value when the motor cycle was at
rest (Speed of sound = 330 ms–1).

A train moving at a speed of 1 220 − ms towards a stationary
object, emits a sound of frequency 1000Hz. 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 ) −1 ms.

An observer is moving towards the stationary source of
sound, then.

A train is moving on a straight track with speed 20 ms–1. It is
blowing its whistle at the frequency of 1000 Hz. The
percentage change in the frequency heard by a person
standing near the track as the train passes him is
(speed of sound = 320 ms–1) close to.