1
Question
A pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fire a gun simultaneously. He hears echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340 ms−1, find the distance between the cliff and the observer :
A pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fire a gun simultaneously. He hears echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340 ms−1, find the distance between the cliff and the observer :
Open in App
Solution
The correct option is C 272 m
The sensation of any sound persists in our ear for about 0.1 seconds. This is known as the persistence of hearing. If the echo is heard within this time interval, the original sound and its echo cannot be distinguished. So the most important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 second after the original sound dies off.
It is given that a pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fire a gun simultaneously. He hears echo from the cliff after 8 vibrations of the pendulum which means that he hears the echo after 1.6 seconds. The speed of sound is given as 340m/s.
The distance traveled by sound of the gun shot in 1.6 seconds is calculated from the formula
Distance traveled =velocityofsound×timetaken. That is, 340×1.6 = 544 m. This is twice the minimum distance between a source of sound (man) and the reflector (cliff) as it is reflected sound.
So, the cliff is at a distance of 272 m least from the man, for the reflected sound or the echo to be heard distinctly in 1.6 seconds.
The sensation of any sound persists in our ear for about 0.1 seconds. This is known as the persistence of hearing. If the echo is heard within this time interval, the original sound and its echo cannot be distinguished. So the most important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 second after the original sound dies off.
It is given that a pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fire a gun simultaneously. He hears echo from the cliff after 8 vibrations of the pendulum which means that he hears the echo after 1.6 seconds. The speed of sound is given as 340m/s.
The distance traveled by sound of the gun shot in 1.6 seconds is calculated from the formula
Distance traveled =velocityofsound×timetaken. That is, 340×1.6 = 544 m. This is twice the minimum distance between a source of sound (man) and the reflector (cliff) as it is reflected sound.
So, the cliff is at a distance of 272 m least from the man, for the reflected sound or the echo to be heard distinctly in 1.6 seconds.
Suggest Corrections
0
Similar questions
Join BYJU'S Learning Program
Explore more
Join BYJU'S Learning Program
