Railway Science (Physics-Sound) (Part-II)

Total Questions: 42

41. What is the wavelength of a sound wave whose frequency is 820 Hz and speed is 420 m/s in a given medium? [RRB ALP Tier - I (30/08/2018) Afternoon]

Correct Answer: (d) 0.52 m
Solution:

Given, Frequency of the sound wave (n) = 820 Hertz (Hz) Speed of sound wave in given medium (v) = 420 m/s The wavelength of sound = λ meters We know that speed of sound v = n × λ Hence by substituting the above values,
we get ⇒ 420 = 820 × λ ⇒ λ = 420/820 = 0.512 m. The value we got is approximately equal to 0.512 m
Hence, the wavelength of the sound wave is λ = 0.512 m (Approx)

42. A sound wave has a frequency of 3.5 kHz and wavelength 0.1 m. How long will it take to travel 700 m? [RRB ALP Tier - I (30/08/2018) Evening]

Correct Answer: (b) 2.0 s
Solution:

Wavelength = 0.1m Frequency = 3.5 kHz = 3500 Hz Velocity (v) = f (Frequency) × λ(wavelength) = 3500 × 0.1=350 m/s Distance = 700m Speed = 350 m/s t = Distance / Speed= 700/350 = 2s