Railway Science (Physics-Waves)

Total Questions: 35

31. What is the relation between frequency and time period? [RRB Group D 10/12/2018 (Morning)]

Correct Answer: (c) T = 1 / v
Solution:

Frequency (v) and Time period (T) can also be expressed as T = 1/๐‘“ or f = 1/๐‘‡

32. A broadcasting station transmits waves with a frequency of 71 ร— 10โด Hz and a speed of 3 ร— 10โธ m/s . The wavelength of the wave is: [RRB ALP Tier - I (17/08/2018) Morning]

Correct Answer: (d) 422.5 m
Solution:

33. If an anchored boat is rocked by waves whose crests are 80 m apart and whose velocity is 20 m/s, then the time required by the crests to reach the boat is _______. [RRB ALP Tier - I (29/08/2018) Morning]

Correct Answer: (b) 4s
Solution:

Time period T is the time taken by a wave to travel the distance between two successive crests or troughs. Also the distance between two successive crests and troughs is the wavelength, ฮป.
Here , given ฮป = 80 m and wave velocity, v = 20 m/s
If f be the frequency of wave so v= fฮป and also f = 1/ ๐‘‡
Thus, T= ฮป/๐‘ฃ = 80/20 = 4s
Therefore, the crest will occur in every 4 second time interval.

34. A boat at anchor is rocked by waves whose consecutive crests are 100 m apart. The wave velocity of the moving crests is 25 ms-1. What is the frequency of rocking of the boat? [RRB ALP Tier - I (29/08/2018) Afternoon]

Correct Answer: (b) 0.25 Hz
Solution:

35. A boat at anchor is rocked by waves whose consecutive crests are 125 m apart. The velocity of the wave of the moving crests is 25 ๐‘š๐‘ โปยน . What is the frequency of the rocking of the boat? [RRB ALP Tier - I (29/08/2018) Evening]

Correct Answer: (c) 0.20 Hz
Solution: