Answer:
The beat frequency is 0.0019 MHz.
Explanation:
Given that,
Velocity = 0.32 m/s
Frequency = 4.40 MHz
Speed of wave = 1540 m/s
We need to calculate the frequency
Case (I),
Observer is moving away from the source
Using Doppler's effect

Where, v' = speed of observer
Put the value into the formula


Case (II),
Cell is as the source of sound of frequency f' and it moving away from the observer.
Using formula of frequency



We need to calculate the beat frequency


Hence, The beat frequency is 0.0019 MHz.
It is the smallest planet with a bluish color that can probably make it look like a comet
The heat (energy) needed to raise the temperature of the water is given by

The wavelength of the radiation of the oven is

, so the energy of a single photon of this radiation is

So, the number of photons required to heat the water is the total energy absorbed by the water divided by the energy of a single photon:

photons