Advertisements
Advertisements
प्रश्न
A person riding a car moving at 72 km h−1 sound a whistle emitting a wave of frequency 1250 Hz. What frequency will be heard by another person standing on the road (a) in front of the car (b) behind the car? Speed of sound in air = 340 m s−1.
Advertisements
उत्तर
Given:
Frequency of whistle \[f_0 = 1250 \text { Hz }\]
Velocity of car \[v_s\] = 72 kmh−1 =\[72 \times \frac{5}{18} = 20 {\text { ms }}^{- 1}\]
Speed of sound in air v = 340 ms−1
(a) When the car is approaching the person:
Frequency of sound heard by the person \[\left( f_1 \right)\] is given by :
\[f_1 = \left( \frac{v}{v - v_s} \right) \times f_0 \]
On substituting the given values in the above equation, we have:
\[f_1 = \frac{340}{340 - 20} \times 1250\]
\[ = 1328 \text { Hz }\]
(b) When the person is behind the car:
Frequency of sound heard by the person \[\left( f_2 \right)\] is given by :
\[f_2 = \left( \frac{v}{v + v_s} \right) \times f_0\]
On substituting the given values in the above equation, we have :
\[f_2 = \left( \frac{340}{340 + 20} \right) \times 1250\]
\[ = \frac{340}{360} \times 1250 = 1181 \text{ Hz }\]
APPEARS IN
संबंधित प्रश्न
Which of the following is a mechanical wave?
Two periodic waves of amplitudes A1 and A2 pass thorough a region. If A1 > A2, the difference in the maximum and minimum resultant amplitude possible is
A wave pulse passing on a string with a speed of 40 cm s−1 in the negative x-direction has its maximum at x = 0 at t = 0. Where will this maximum be located at t = 5 s?
Choose the correct option:
A standing wave is produced on a string clamped at one end and free at the other. The length of the string ______.
A string of linear mass density 0⋅5 g cm−1 and a total length 30 cm is tied to a fixed wall at one end and to a frictionless ring at the other end (See figure). The ring can move on a vertical rod. A wave pulse is produced on the string which moves towards the ring at a speed of 20 cm s−1. The pulse is symmetric about its maximum which is located at a distance of 20 cm from the end joined to the ring. (a) Assuming that the wave is reflected from the ends without loss of energy, find the time taken by the string to region its shape. (b) The shape of the string changes periodically with time. Find this time period. (c) What is the tension in the string?
A piano wire weighing 6⋅00 g and having a length of 90⋅0 cm emits a fundamental frequency corresponding to the "Middle C" \[\left( \nu = 261 \cdot 63 Hz \right)\]. Find the tension in the wire.
A cylindrical metal tube has a length of 50 cm and is open at both ends. Find the frequencies between 1000 Hz and 2000 Hz at which the air column in the tube can resonate. Speed of sound in air is 340 m s−1.
In a resonance column experiment, a tuning fork of frequency 400 Hz is used. The first resonance is observed when the air column has a length of 20.0 cm and the second resonance is observed when the air column has a length of 62.0 cm. (a) Find the speed of sound in air. (b) How much distance above the open end does the pressure node form?
Two successive resonance frequencies in an open organ pipe are 1944 Hz and 2592 Hz. Find the length of the tube. The speed of sound in air is 324 ms−1.
Calculate the frequency of beats produced in air when two sources of sound are activated, one emitting a wavelength of 32 cm and the other of 32.2 cm. The speed of sound in air is 350 m s−1.
The horn of a car emits sound with a dominant frequency of 2400 Hz. What will be the apparent dominant frequency heard by a person standing on the road in front of the car if the car is approaching at 18.0 km h−1? Speed of sound in air = 340 m s−1.
A train approaching a platform at a speed of 54 km h−1 sounds a whistle. An observer on the platform finds its frequency to be 1620 Hz. the train passes the platform keeping the whistle on and without slowing down. What frequency will the observer hear after the train has crossed the platform? The speed of sound in air = 332 m s−1.
A small source of sound vibrating at frequency 500 Hz is rotated in a circle of radius 100/π cm at a constant angular speed of 5.0 revolutions per second. A listener situation situates himself in the plane of the circle. Find the minimum and the maximum frequency of the sound observed. Speed of sound in air = 332 m s−1.
A car moving at 108 km h−1 finds another car in front it going in the same direction at 72 km h−1. The first car sounds a horn that has a dominant frequency of 800 Hz. What will be the apparent frequency heard by the driver in the front car? Speed of sound in air = 330 m s−1.
Two sources of sound are separated by a distance of 4 m. They both emit sound with the same amplitude and frequency (330 Hz), but they are 180° out of phase. At what points between the two sources, will the sound intensity be maximum?
The speed of a transverse wave in an elastic string is v0. If the tension in the string is reduced to half, then the speed of the wave is given by:
Change in temperature of the medium changes ______.
