Q.
A police car moving at$22\ ms^{- 1}$, changes a motorcyclist. The police man sounds his horn at 176 Hz, while both of them move towards a stationary siren of frequency 165 Hz. Calculate the speed of the motorcycle, if it is given that he does not observe any beats.
A) $33ms^{- 1}$
B) $22\ ms^{- 1}$
C) Zero
D) $11ms^{- 1}$
Explanation
(b) The motorcyclist observes no beats. So the apparent frequency observed by him from the two sources must be equal.
$\therefore 176\ \left( \frac{330 - v}{330 - 22} \right) = 165\ \left( \frac{330 + v}{330} \right)$
Solving this equation we get,
$v = 22ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.