Exam

JEE Main

Year

2019

Date

12 April

Shift

Evening Shift

Subject

Physics

Chapter

Waves and Sound

JEE Main 2019 · 12 April · Evening Shift · Physics · Waves and Sound

Two sources of sound S _ 1 and S _ 2 produce sound waves of same...

Two sources of sound ${S}_{1}$ and ${S}_{2}$ produce sound waves of same frequency $660Hz .$ A listener is moving from source ${S}_{1}$ towards ${S}_{2}$ with a constant speed ${u}_{0}m / s$ and he hears $10beats / s .$ The velocity of sound is $330m / s .$ Then, ${u}_{0}$ equals:

Step-by-step solution

Frequency observed from ${S}_{1}: {f}_{1} = 660\left(\dfrac{330 - {u}_{0}}{330 - 0}\right)$
Frequency observed from ${S}_{2}: {f}_{2} = 660\left(\dfrac{330 + {u}_{0}}{330 - 0}\right)$
As ${f}_{2} - {f}_{1} = 10$
$660\left[\dfrac{330 + {u}_{0}}{330 - 0} - \dfrac{330 - {u}_{0}}{330 - 0}\right] = 10$
$2\left(2{u}_{0}\right) = 10$
${u}_{0} = 2.5m / s$