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The MCQs below are drawn from the Physics subject category.
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911
The speed of hypersonic missile is _____ times the speed of sound, as reported by US Navy?
A. 20 times
B. 15 times
C. 5 times
D. 10 times
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Correct Option
Explanation
The source block's provided answer hint indicates option B as the correct choice for this item.
912
A tuning fork A produces 4 beats per second with another tuning fork B. It is found that by loading B with some wax, the beat frequency increases to 6 beats per second. If the frequency of A is 320 Hz, then the frequency of B when loaded is
A. 316 Hz
B. 314 Hz
C. 326 Hz
D. 324 Hz
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Correct Option
Explanation
Originally B must have been 316 Hz (|320-316|=4); loading lowers its frequency further to 314 Hz giving |320-314|=6 beats.
913
Velocity of sound in air is
A. 3 × 10^-? metre per second
B. 300 meters per second
C. 3 × 10^2 meters per second
D. 3 × 10^? metres per second
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Correct Option
Explanation
Standard approximate value for speed of sound in air at NTP is about 300 m/s.
914
Which of the following properties of sound is affected by change in air temperature?
A. Intensity
B. Wavelength
C. Frequency
D. Amplitude
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Correct Option
Explanation
Air temperature changes the speed of sound; for a constant source frequency this changes the wavelength of the sound.
915
The vibrations taking place in the diaphragm of a microphone will be
A. damped vibrations
B. forced vibrations
C. free vibrations
D. electrically maintained vibrations
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Correct Option
Explanation
The diaphragm vibrates in response to incoming sound waves (external driving force), so these are forced vibrations.
916
In gases, the speed of sound is inversely proportional to ____ density when other factors are same.
A. Square root.
B. Square.
C. Third power.
D. Third root.
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Correct Option
Explanation
The speed of sound in a gas varies inversely with the square root of density (for fixed temperature and composition), and the OCR shows a mark by option A.
917
Assume that the velocity of sound in air is 330 m s^-1. What will be the time interval between the two loudest echoes?
A. 1/3 s
B. 5/6 s
C. 1/6 s
D. 2/3 s
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Correct Option
Explanation
Using the distances to two cliffs (110 m and 165 m) the difference in round-trip times is 2*(165-110)/330 = 1/3 s, so 1/3 s is the interval.
918
A sound wave has frequency 500 Hz and velocity 350 m s^-1. What is the distance between the two particles having phase difference of 60° ?
A. 120.0 cm
B. 0.7 cm
C. 70 cm
D. 12.0 cm
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Correct Option
Explanation
Wavelength λ = v/f = 350/500 = 0.7 m; distance for 60° (1/6 λ) = 0.7/6 ≈ 0.1167 m ≈ 12.0 cm.
919
Sound cannot travel through:
A. Liquids
B. Gases
C. Vacuum
D. Solids
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Correct Option
Explanation
Sound requires a medium to travel, and cannot travel through a vacuum, so option B is correct.
920
Two tuning forks have frequencies 450 Hz and 454 Hz respectively. On sounding the forks together, the time interval between successive maximum intensities will be
A. 1/2 second
B. 2 second
C. 1 second
D. 1/4 second
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Correct Option
Explanation
Beat frequency = |450 - 454| = 4 Hz, so time between maxima = 1/4 s, hence option A is correct.
