A boat is travelling in a river with a speed of 10m/s along the stream flowing with a speed 2m/s. From this boat, a sound transmitter is lowered into the river through a rigid support. The wavelength of the sound emitted from the transmitter inside the water is 14.45mm. Assume that attenuation of sound in water and air is negligible.
a. What will be the frequency detected by a receiver kept inside downstream?
b. The transmitter and the receiver are now pulled up into air. The air is blowing with a speed of 5m/s in the direction opposite the river stream. Determine the frequency of the sound detected by the receiver.
(Temperature of the air and water is 20∘C; density of river water is 103kg/m3 ; bulk modulus of the water is 2.088×109 Pa, gas constant R = 8.31J/mol – K; mean molecular mass of air is for air is 28.8×10−3 kg/mol: cpcv for air is 1.4.)