
Concept explainers
A yellow submarine traveling horizontally at 11.0 m/s uses sonar with a frequency of 5.27 × 103 Hz. A red submarine is in front of the yellow submarine and moving 3.00 m/s relative to the water in the same direction. A crewman in the red submarine observes sound waves (“pings”) from the yellow submarine. Take the speed of sound in seawater as 1 533 m/s. (a) Write Equation 14.12. (b) Which submarine is the source of the sound? (c) Which submarine carries the observer? (d) Does the motion of the observer’s submarine increase or decrease the time between the pressure maxima of the incoming sound waves? How does that affect the observed period? The observed frequency? (e) Should the sign of v0 be positive or negative? (f) Does the motion of the source submarine increase or decrease the time observed between the pressure maxima? How does this motion affect the observed period? The observed frequency? (g) What sign should be chosen for vs? (h) Substitute the appropriate numbers and obtain the frequency observed by the crewman on the red submarine.
(a)

Answer to Problem 36P
The equation 14.12 in the text book is,
f0=fs(v+v0v−vs)
- fs is the frequency emitted by the source
- f0 is the frequency detected by the observer
- v is the speed of the wave in the propagating medium
- v0 is the velocity of the observer relative to the medium
- vs is the source’s velocity relative to the propagating medium
Explanation of Solution
The equation 14.12 in the text book is,
f0=fs(v+v0v−vs)
- fs is the frequency emitted by the source
- f0 is the frequency detected by the observer
- v is the speed of the wave in the propagating medium
- v0 is the velocity of the observer relative to the medium
- vs is the source’s velocity relative to the propagating medium
Conclusion:
The equation 14.12 in the text book is,
f0=fs(v+v0v−vs)
- fs is the frequency emitted by the source
- f0 is the frequency detected by the observer
- v is the speed of the wave in the propagating medium
- v0 is the velocity of the observer relative to the medium
- vs is the source’s velocity relative to the propagating medium
(b)

Answer to Problem 36P
Explanation of Solution
The yellow submarine emits the sound.
Thus, the source of sound is the yellow submarine.
Conclusion:
The source of sound is yellow submarine.
(c)

Answer to Problem 36P
Explanation of Solution
The observer is standing in the red submarine and observing the sound wave coming from the yellow submarine.
Thus, the red submarine is carrying the observer.
Conclusion:
The red submarine is carrying the observer.
(d)

Answer to Problem 36P
Explanation of Solution
Since, the submarine carrying the observer is moving; the observer is also moving. The observer is moving away from the observer. So, this will increase the total time observed between the arrivals of successive pressure maxima. This effect will decrease the observed frequency and an increase in the observed period.
Thus, the observers submarine increase the time between the pressure maxima of the incoming sound waves.
Conclusion:
The observers submarine increase the time between the pressure maxima of the incoming sound waves.
(e)

Answer to Problem 36P
Explanation of Solution
Given Info:
f0=fs(v+v0v−vs)
- fs is the frequency emitted by the source
- f0 is the frequency detected by the observer
- v is the speed of the wave in the propagating medium
- v0 is the velocity of the observer relative to the medium
- vs is the source’s velocity relative to the propagating medium
Since, the observed frequency is decreasing; the sign of the variable v0 should be negative in the above equation.
Thus, the sign of the velocity of the observer relative to the medium ( v0) is negative.
Conclusion:
The sign of the velocity of the observer relative to the medium ( v0) is negative.
(f)

Answer to Problem 36P
Explanation of Solution
Given Info:
Since, the source submarine is moving towards the observer; the time between the arrivals of successive pressure maxima will be decreasing. Thus, the observed period will be increasing and the observed frequency will also be increasing.
Thus, the time between the arrivals of the successive pressure maxima will decrease. The observed period and the frequency will be increasing.
Conclusion:
The time between the arrivals of the successive pressure maxima will decrease. The observed period and the frequency will be increasing.
(g)

( vs).
Answer to Problem 36P
Explanation of Solution
Given Info:
f0=fs(v+v0v−vs)
- fs is the frequency emitted by the source
- f0 is the frequency detected by the observer
- v is the speed of the wave in the propagating medium
- v0 is the velocity of the observer relative to the medium
- vs is the source’s velocity relative to the propagating medium
Since, the observed frequency is increasing; the denominator of the above equation should be decreasing. Thus, the sign of the source’s velocity relative to the propagating medium ( vs) should be positive.
Thus, the sign of the source’s velocity relative to the propagating medium ( vs) should be positive.
Conclusion:
The sign of the source’s velocity relative to the propagating medium ( vs) should be positive.
(h)

Answer to Problem 36P
Explanation of Solution
Given Info:
The speed of the yellow submarine is 11.0 m/s.
The frequency of the sonar is 5.27×103 Hz.
The speed of the red submarine is 3.0 m/s relative to the water in the same direction.
The speed of the sound in sea water is 1533 m/s.
Formula to calculate the frequency of the crewman is,
f0=fs(v+v0v−vs)
- fs is the frequency emitted by the source
- f0 is the frequency detected by the observer
- v is the speed of the wave in the propagating medium
- v0 is the velocity of the observer relative to the medium
- vs is the source’s velocity relative to the propagating medium
Substitute 5.27×103 Hz for fs, 1533 m/s for v, −3.0 m/s for v0 and 11.0 m/s for vs to find the frequency of the crew man,
f0=(5.27×103 Hz)(1533 m/s+(−3.0 m/s)1533 m/s−11.0 m/s)=5.30×103 Hz
Thus, the frequency observed by the crewman on the red submarine is 5.30×103 Hz
Conclusion:
The frequency observed by the crewman on the red submarine is 5.30×103 Hz.
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Chapter 14 Solutions
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