An airplane flying at a constant speed of 200m/s emits a 1000Hz tone. At a particular instant, the airplane’s velocity is perpendicular to the line joining the airplane and a ground observer. What frequency does the observer hear at that instant? (Take the speed of sound in air to be 340m/s.)
a) 1176Hz
b) 1588Hz
c) 1000Hz
d) 824Hz