A train is moving on a straight track with speed 20 ms^(-1). It is blowing whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is close to (speed of sound = 320 ms^(-1)).

A train is moving on a straight track with speed 20 ms^(-1). It is blo

1.	A train is moving on a straight track with speed 20 ms^(-1). It is blowing whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is close to (speed of sound = 320 ms^(-1)).
Answer» `6%` `12%` `18%` `24%` Solution :When train MOVES towards STATIONARY listener, `(f _(L))/( v + v _(L)) = (f _(S))/( v + v _(S))` `therefore (f _(L))/( 320 + 0) = (1000)/(320 - 20) implies f _(L) = 1000 xx (320)/(300)` `therefore f _(L) = 1067 Hz` (ii) When train moves away from stationary listener `(f ._(L))/( v + v _(L)) = (f _(S))/( v +v _(S))` ` therefore (f ._(L))/( 320 +0) = (1000)/( 320 + 20) implies f._(L) = 1000 xx (320)/(340) ` `therefore f._(L) = 941 Hz` Percentage DECREASE in frequency of sound heard by listener, `(f _(L)-f ._(L))/( f _(L)) xx 100 %= (1067 - 941)/( 10 67) xx 100 %` `= 11. 8 % = 12%`