What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?

when observer and source moves relative to each other then the frequency received by the observer is different from the real frequency

This apparent change in frequency due to relative motion is known as Doppler's effect.

Here we know that

here we know that

= real frequency

v = speed of sound

= speed of observer

= speed of source

so this is known as Doppler's Effect

answer: at 24 february, 2014 the population gets twice of its initial population.

explanation:

since we have given that

the population for alpha city, t years after january 1, 2004 is given as

first we find out the initial population, i.e. t=0,

so, our quadratic equation becomes,

according to question, we have said that if the population has twice its initial population, then it becomes

so, time taken to reach this above mentioned population is given by

now, we know that time can't be negative so, we take t=9.149 years.

hence, at 24 february, 2014 the population gets twice of its initial population.