Tina is waiting at the bus stop. she sees and hears an ambulance as it approaches and passes by her. which two changes in the loudness of the siren does tina hear?
a. the sound becomes less loud as the ambulance approaches her.
b. the sound becomes louder as the ambulance approaches her.
c. the loudness of the sound remains the same as long as she can see the ambulance.
d. the sound stops when it reaches her.
e. the sound becomes less loud as the ambulance moves away from her.

Option B i.e The sound becomes louder as the ambulance approaches her,

Option E i.e The sound becomes less loud as the ambulance moves away from her, are the two changes in the the loudness of the Siren which Tina would hear.

The above changes are due to the Doppler Effect. According to Doppler Effect, effective wavelength is shortened when an approaching source moves closer during the period of sound wave and thus gives a higher pitch.  Likewise the pitch of a receding sound source will be lowered.

the right is separation by density .

take the blood which is a good example of a heterogeneous mixture.

blood is a vital liquid in our body, which transports oxygen from the air to our lungs so we can breathe. it is also used to eject wastes, such as carbon dioxide, to bring cells and molecules of the immune system to the tissues, and to spread hormones throughout the body. it corresponds to plasma, red blood cells, white blood cells, platelets and hemoglobins combined.

in medical tests centrifugal force is used to separate the different components of the blood.

in general, the centrifugation will allow to separate and analyze the different components of the blood, to know if the rate of white blood cells in the blood of a patient, for example, is normal, and therefore to know if his system immune is integrity.

under the action of centrifugal force, the solid components in the blood are drawn to the bottom of the tube in which the blood is contained. the centrifugal force then acts as an accelerated settling. it separates plasma from red blood cells and white blood cells.

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