Apolice siren sounds different as it comes close to you than when it moves away from you. what term explains how this happens?
a. diffraction
b. the doppler effect
c. rarefaction
d. shockwaves

b. the Doppler effect

Explanation:

Doppler effect describes the apparent change in the frequency heard by the listener than the frequency emitted by the source when there is relative motion between the two. When the source and listener approach each other, the apparent frequency is higher than the source and when they move away, the apparent frequency heard by the listener is lower than the source.

Due to Doppler's effect, a police siren sounds different when it comes closer than when it moves away. When it is closer, higher pitch can be heard than when it is moving past away.

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.