Question

A sound has 13 crests and 15 troughs in 3 seconds. When the second crest is produced the first is 2cm away from the source? Calculate

Answer 1

1. It means it travel 15 waves in 3sec

So, In 1sec. ==> 15/3

= 5 waves it travel.

So, Its frequency is 5Hz.

2. Wave length ( W.L. ) ==> 2cm/100

= 0.02 m

3. Wave speed ==> Frequency × W.L.

= 0.02 × 5

= 0.1 m/s

Answer 2

a) Wavelength = distance between two consecutive crests or trough =2cm

b) frequency = no. of troughs/time

= 15/3 = 5 Hz

c) distance travelled by wave = 15×2= 30cm

Time= 3 seconds

.: Wave speed = distance/time

= 30/3 = 10 cm/s

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