The correct option is A 5 s
Given:
Wavelength of sound wave, λ=40 cm=0.4 m
Time period, T=0.0005 s
Distance travelled, s=4 km=4000 m
Let speed of sound wave be v.
Speed of a wave is the product will be:
v=λT
v=0.4 m0.0005 s
v=800 ms−1
Let the time taken for the wave to travel distance s be t.
From definition of speed,
v=st
t=sv
t=4000800=5 s