Question:easy
A train is moving towards a stationary observer with speed \(34\) m/s. A train sounds a whistle of frequency \(450\) Hz. If the speed of sound is \(340\) m/s, the frequency heard by the observer in Hz is
A train is moving towards a stationary observer with speed \(34\) m/s. A train sounds a whistle of frequency \(450\) Hz. If the speed of sound is \(340\) m/s, the frequency heard by the observer in Hz is
Show Hint
Source moving toward a stationary observer: f = f0 v/(v - vs).
Updated On: Oct 1, 2026
- \(440\)
- \(480\)
- \(500\)
- \(540\)
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Use wavelength compression:
In one period $\frac1{450}$ s, the train advances $\frac{34}{450}$ m, shortening the wavelength: $\lambda' = \frac{340}{450} - \frac{34}{450} = \frac{306}{450}$ m.
Step 2: Observed frequency:
$f' = \frac{v}{\lambda'} = \frac{340\times450}{306} = 500$ Hz.
Step 3: Sign check:
The frequency is higher than 450 Hz, as expected for an approaching source.
Final Answer:
The observer hears 500 Hz, option (C). \[ \boxed{500\text{ Hz}} \]
In one period $\frac1{450}$ s, the train advances $\frac{34}{450}$ m, shortening the wavelength: $\lambda' = \frac{340}{450} - \frac{34}{450} = \frac{306}{450}$ m.
Step 2: Observed frequency:
$f' = \frac{v}{\lambda'} = \frac{340\times450}{306} = 500$ Hz.
Step 3: Sign check:
The frequency is higher than 450 Hz, as expected for an approaching source.
Final Answer:
The observer hears 500 Hz, option (C). \[ \boxed{500\text{ Hz}} \]
Was this answer helpful?
0
Top Questions on doppler effect
- A passenger is sitting in a fast moving train. The engine of the train blows a whistle of frequency N. If the apparent frequency of sound heard by the passengers is \( N' \), then:
- MHT CET - 2025
- Physics
- doppler effect
- A car P travelling at 20 \(ms^{–1}\) sounds its horn at a frequency of 400 Hz. Another car Q is travelling being the first car in the same direction with a velocity 40 \(ms^{–1}\) . The frequency heard by the passenger of the car Q is approximately [Take, velocity of sound = 360 \(ms^{–1}\) ]
- JEE Main - 2023
- Physics
- doppler effect
- A source has wavelength 60 cm when it is stationary. If the speed of sound in air is 320m s⁻¹ and the source moves with speed 20m s⁻¹, the wavelength in the forward direction will be
- BITSAT - 2010
- Physics
- doppler effect
A source of sound S emitting waves of frequency 100Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4m s⁻1 at an angle of 60^∘ with the source–observer line as shown in the figure. The observer is at rest. Find the apparent frequency observed by the observer. (Velocity of sound in air =330m s⁻1).
- BITSAT - 2020
- Physics
- doppler effect
- Want to practice more? Try solving extra ecology questions todayView All Questions