A train standing at the outer singal of a railway station blows a whistle of frequency 400 Hz in still air. (i) What is frequency of the whistle for a platform observer when the train (a) approaches the platform with a speed of 10 m/s, (b) recedes from the platform with a speed of 10 m/s. (ii) What is the speed of sound in each case if the speed of sound in still air is 340 m/s.

A train standing at the outer singal of a railway station blows a whis

1.	A train standing at the outer singal of a railway station blows a whistle of frequency 400 Hz in still air. (i) What is frequency of the whistle for a platform observer when the train (a) approaches the platform with a speed of 10 m/s, (b) recedes from the platform with a speed of 10 m/s. (ii) What is the speed of sound in each case if the speed of sound in still air is 340 m/s.
Answer» SOLUTION :(i) Here, n= 400 HZ, `v = 340 m//s` (a) When train APPROACHES the platform, `v_(s) = 10 m//s` So, required frequency `=v/(v-v_(s))xxn=(340xx400)/(340-10)=412.12" Hz"` (b) When train recedes from the platfrom. `v_(s) = 10 m//s` Hence, required frequency `=v/(v-v_(s))xxn=(340xx400)/(340+10)= 388.6" Hz"` (ii) The SPEED of sound in both the cases is same.