Amoving sound source a has a velocity (85 km/hr) \widehat{i\ } and a moving reflecting surface b has a velocity (75 km/hr) (-\ \widehat{i\ }). the source a emits a sound with a frequency of 39 khz. a) assuming b is approaching a find the frequency as heard by b b) assuming b is moving away from a, find the frequency as heard by b c) what is the frequency of the reflected beam to the source (pick (b) as the set-up to answer this question). speed of sound in air 340 m/s