Question

Thinequency of the sound heard by the motorcyclist is given by the expression A motorcyclist moves to the right with a speed of 20 m/s. A police car with velocity 30 m/s to the left emits a sound with a frequency of 400 Hz. Speed of sound in air is 340 m/s.

Answer 1

" The general a Dopp formula for Doppler etted is given by, fo=f f ( a VI VD V + vs where vis source the sound velocity Nos observere detector velocity Vsa veloeily f = frequeney of the sound emitted by the source fo frequency observed by the defecton / observer car are moving to ward Here Here, both the motorcyclist and the palice each other. Hence, į is evident that the the absored hoop observed by the motoney clist will be wigher. Hence, the Connect expression ☺ now becomes in this case fos f frequency Vt No V-Vg This is the nequined expression. Now given, N340 m/s Vo = velocity of the motoncyclist = 20 m/s Vs a velocity of the police car 30 m/s f = frequeney of the sound emitted by the police car = 400 Hz

( S 464.52 Hz 464.52 ltz then 340 + 20 fo: 400 Hz 340-30 = 400 x 1360 310 Hence, observed frequency is Note: If the motoneyclist the police can were moving moving away other then the would would become fo=fs V-VD fo vt us Here the observed frequency to is lower than because denominaton is greater than the numeraton. each and away from equation el