a man standing on railway platform listening to the whistle of an engine tat passes the man at constant speed at time t'' .

Hoow does the frequency as heard by man changes wid time.

Sketch the graph of f vs t.

frequency heard by listener from t=0 (when train was approaching and was far apart ) to t=T (when train passes the listener) is constant & given by

f = f_o(V/V-V_t)                      (V_t = speed of train, V speed of sound)

when train has passed the listener then frequency again becomes constant but now it is f¹

f¹ = f_o(V/V+V_t)

now plot this graph by using these two eq