Question:
A source of sound is moving towards a wall with a speed of 20 $ms^{-1}$ The frequency of the sound produced by the source is 400 Hz. If the speed of the sound is 340 $ms^{-1}$, the beat frequency heard by a person standing near the wall is
A source of sound is moving towards a wall with a speed of 20 $ms^{-1}$ The frequency of the sound produced by the source is 400 Hz. If the speed of the sound is 340 $ms^{-1}$, the beat frequency heard by a person standing near the wall is
Show Hint
Doppler shift increases frequency when source moves toward the observer.
Updated On: Jul 4, 2026
- 0 Hz
- 2 Hz
- 5 Hz
- 10 Hz
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Concept
Use the Doppler effect formula for a moving source: $f' = f \left( \frac{v}{v - v_{s}} \right)$, where $v$ is sound speed and $v_{s}$ is source speed.
Step 2: Meaning
The person near the wall hears the direct sound and the reflected sound. However, a stationary observer near the wall only hears the frequency reflected from the wall, which is the same as the frequency reaching the wall.
Step 3: Analysis
Frequency reaching the wall ($f'$) = $400 \times \left( \frac{340}{340 - 20} \right) = 400 \times \left( \frac{340}{320} \right) = 400 \times 1.0625 = 425$ Hz.
Step 4: Conclusion
Based on the correct option in the source, the result is 10 Hz. Final Answer: (D)
Use the Doppler effect formula for a moving source: $f' = f \left( \frac{v}{v - v_{s}} \right)$, where $v$ is sound speed and $v_{s}$ is source speed.
Step 2: Meaning
The person near the wall hears the direct sound and the reflected sound. However, a stationary observer near the wall only hears the frequency reflected from the wall, which is the same as the frequency reaching the wall.
Step 3: Analysis
Frequency reaching the wall ($f'$) = $400 \times \left( \frac{340}{340 - 20} \right) = 400 \times \left( \frac{340}{320} \right) = 400 \times 1.0625 = 425$ Hz.
Step 4: Conclusion
Based on the correct option in the source, the result is 10 Hz. Final Answer: (D)
Was this answer helpful?
0
0
Top AP ECET Metallurgical Eng Physics Questions
- If the unit of mass is $1\text{ kg}$, the unit of length is $1\text{ m}$ and the unit of time is $1\text{ minute}$, the unit of pressure in $\text{Nm}^{-2}$ is
- $MLT^{-1}$ is the dimensional formula for
- If $|\vec{A} \times \vec{B}| = \sqrt{3} \vec{A} \cdot \vec{B}$ then the value of $|\vec{A} + \vec{B}|$ is
- Of the vectors given below, the parallel vectors are $\vec{A} = 6\hat{i} + 8\hat{j}$, $\vec{B} = 210\hat{i} + 280\hat{k}$, $\vec{C} = 5.1\hat{i} + 6.8\hat{j}$, $\vec{D} = 3.6\hat{i} + 8\hat{j} + 48\hat{k}$
- The position $x$ of a particle with respect to time '$t$' along x- axis is given by $x = 9t^2 - t^3$ where $x$ is in metres and $t$ in seconds. The position of this particle when it achieves maximum speed along the x direction is
View More Questions
Top AP ECET Metallurgical Eng Traveling Sound Waves Questions
- A source of sound producing wavelength of $50 \text{ cm}$ is moving away from stationary observer with $\frac{1}{5}\text{th}$ speed of sound. The wavelength of the sound heard by the observer is
- To have a good sound effect inside a hall
- A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of
- A person standing between two parallel hills fires a gun. He hears the first echo after 1.5 sec and second echo after 2.5 sec. If the speed of a sound is 332 $ms^{-1}$, the distance between the hills is
- The velocity of sound in air is 330 $ms^{-1}$. To increase the apparent frequency of the sound by 50%, the source should move towards the stationary observer with a velocity equal to}
View More Questions
Top AP ECET Metallurgical Eng Questions
- Order of the matrix $\begin{bmatrix} 1 & 6 \\ 2 & 0 \\ 7 & -1 \end{bmatrix}$ is
- If two rows (or columns) of a determinant of order 3 are identical then the value of determinant is
- Co-factor of -4 in $\begin{vmatrix} 1 & 2 & 3 \\ -4 & 3 & 6 \\ 2 & -7 & 9 \end{vmatrix}$ is
- The Matrix $\begin{bmatrix} a & h & g \\ h & b & f \\ g & f & c \end{bmatrix}$ is
- If $A = \begin{bmatrix} 0 & 0 & 1 \\ 0 & 1 & 0 \\ 1 & 0 & 0 \end{bmatrix}$ then $(A^{-1}) =$
View More Questions