Q. Suppose that the speed of sound in air at a given temperature is $400\ m/sec.$ An engine blows a whistle at $1200\ Hz$ frequency. It is approaching an observer at the speed of $100\ m/sec.$ What is the apparent frequency as heard by the observer
A) $600\ Hz$
B) $1200\ Hz$
C) $1500\ Hz$
D) $1600\ Hz$
Explanation
(d) $n^{'} = n\left( \frac{v}{v - v_{S}} \right) = 1200\left( \frac{400}{400 - 100} \right) = 1600\ Hz$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.