AMU Engineering 2018 solved paper Solved Paper

Given, speed of rocket, v1=200m∕s
Frequency emitted by the rocket, v1=1000Hz
Velocity of sound, vsound =330m∕s
In Ist case, Apply Doppler's effect in sound's equation.
v=

v+uo

v−us

Putting values,
v1=

330+0

330−200

×1000
v1=

33

13

×1000Hz ........(i)
This frequency is reflected back to the rocket.
In IInd case. Apply Doppler's effect in sound's equation
v2=

330+200

330

v1
=

530

330

×

33

13

×1000‌‌‌‌ [from Eq. (i)]
=

53

13

×1000=4076.92Hz
Thus, the most appropriate option is (d).