Waves (Physics)

Total Questions: 43

41. What is the approximate speed of sound in distilled water at 25°C (77°F)? [S.S.C Online CHSL (T-I) 12.10.20 (Shift-II)]

Correct Answer: (d) 1498 m/s
Solution:

The approximate speed of sound in distilled water at 25°C (77°F) is 1498 meters per second (m/s).

This is significantly faster than the speed of sound in air because water is much denser and less compressible than air. 

42. In fluid mechanics, the Mach number will be 1 if the speed of the object is equal to ________ . [S.S.C Online C.P.O.S.I (T-1) 5.07.2017 (Shift-II)]

Correct Answer: (c) the speed of sound
Solution:

In fluid mechanics, the Mach number will be 1 if the speed of the object is equal to the speed of sound in the surrounding fluid.

The Mach number (M) is defined as the ratio of the flow speed past a boundary to the local speed of sound. Mathematically:
where:
(v) is the local flow velocity (the speed of the object relative to the fluid).
(a) is the local speed of sound in the fluid medium.
Therefore, when
(v = a), the Mach number (M) becomes 1.
This condition is often referred to as sonic speed.

43. The sound of thunder is heard much later than the flash of light is seen. What does this show? [S.S.C. Online MTS (T-1) 27.10.2021 (Shift-II)]

Correct Answer: (a) The speed of sound is much less than the speed of light.
Solution:During discharging in clouds, thunder and lightning are produced simultaneously, but the speed of light is many times greater than that of sound, due to which light reaches us first, so the glow appears first and the thunder of the clouds is heard later.