question_answer 37)

                  A train whistling at constant frequency is moving towards a station at a constant speed V. The train goes past a stationary observer on the station. The frequency \[n'\] of the sound as heard by the observer is plotted as a function of time \[t\] (Fig ). Identify the expected curve.                 (a)       (b)                 (c)        (d)

Answer:

                  (b) When train approaches towards a stationary observer, frequency \[x'\] of the sound heard by observer increases and becomes maximum, when the train first passes the observer. Thereafter, frequency \[x'\] decreases as the train moves away from die observer.