Exam

JEE Main

Year

2015

Date

10 April

Mode

Online

Subject

Physics

Chapter

Waves and Sound

JEE Main 2015 · 10 April · Online · Physics · Waves and Sound

A bat moving at 10ms^ - 1 towards a wall sends a sound signal of...

A bat moving at $10ms^{- 1}$ towards a wall sends a sound signal of $8000\text{Hz}$ towards it. On reflection, it hears a sound of frequency $f$. The value of $f$ in $\text{Hz}$ is close to
$( \text{speed of sound} = 320ms^{- 1} )$

Step-by-step solution

We can assume that reflected wave is due to image of $\text{B}$ coming with same speed in opposite direction

Observer

$f = \dfrac{v + 10}{v - 10} \times {f}_{0}$

$= \dfrac{320 + 10}{320 - 10} \times 8000$

$= \dfrac{330}{310} \times 8000$

$= \dfrac{33}{31} \times 8000$

$= 8516Hz$