Question

a train is approaching a station at 90 km per hour sounding a whistle of frequency thousand Hertz what will be the Apparent frequency here by the listeners sitting on the platform if the train moves away from the station with the same speed​

Answer 1

Answer:

Explanation:

Given  

A train is approaching a station at 90 km per hour sounding a whistle of frequency thousand Hertz what will be the Apparent frequency here by the listeners sitting on the platform if the train moves away from the station with the same speed

We know that speed of sound = 340 m/s

So frequency of source = fo = 1000 hz

Speed of train u = 90 km / h = 90,000 / 3600 = 25 m/s

Now when train is approaching , using the relation we get

f = [v / (v – u) ] fo

 = [340 / (340 – 25) ]1000  

= [340 / 315 ] 1000

= 1.07936 x 1000

= 1.079.36 hz

Now when train is moving away, using the relation we get

f = [v / (v – u)] fo

f = [340 / (340 + 25)] 1000

  = [340 / 365 ] 1000

  = 0.9315 x 1000

  = 931.506 hz

Answer 2

Answer:

Explanation:

As,

speed of sound = 90km\h

 =90×1000

 =25m\

frequency of source=1000HZ

speed of sound = 340m\

apparent freq .=?

and f' apparent frquency when train moves away fromstation .

formula,

 f'=

 -------- : us=speed of trainf'

 v-us

f=340/340-25×1000

=1079.4Hz

f'=

-----------

v+us

=340/340+25

=931.5Hz