The pitch of the whistle of an engine appears to drop by 20 % of original value when it passes a stationary observer. If speed of sound in air 350 ~m / s , then speed of engine in m / s is

Step-by-step solution

Aparent pitch heard by the observer f ^ = 4 5 f where, f is the original pitch of the engine. As the apparent frequency is lowered, thus the engine must be moving away from the stationary observer. From Doppler effect, apparent frequency heard: aligned & f ^ = f [ V _ sound V _ sound + V _ source ] & 4 f 5 = [ 350 350+ V _ Source ] & V _ Source =87.5 aligned