Answer:
b) 472HZ, 408HZ
Explanation:
To find the frequencies perceived when the bus approaches and the train departs, you use the Doppler's effect formula for both cases:
fo: frequency of the source = 440Hz
vs: speed of sound = 343m/s
vo: speed of the observer = 0m/s (at rest)
v: sped of the train
f: frequency perceived when the train leaves us.
f': frequency when the train is getTing closer.
Thus, by doing f and f' the subjects of the formulas and replacing the values of v, vo, vs and fo you obtain:
hence, the frequencies for before and after tha train has past are
b) 472HZ, 408HZ
<h2>Answer: decibels
</h2>
The decibel 
is the relation between two values: the pressure produced by a sound wave and a pressure taken as a reference. Resulting in a dimensionless value.
It should be noted that itself<u> is not a unit of measure</u>, since in reality the unit is bel 
(which <u>is not part of the International System of Units</u>) in honor of Alexander Graham Bell.
However, given the amplitude of the measured elements in practice, its submultiple, the decibel, is used. That is, this quotient is a logarithmic expression, where 
<span>Here is an example, the allele for blue eyes and the allele for brown eyes are different versions of the gene for eye color. Alleles are located at the same genetic locus . </span>
Answer:
ثر أنواع التربة خصوبة التربحمراء .
ج- السوداء
Explanation:
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