Answer:

Explanation:
We know that speed is defined as distance moved per unit time hence expressed as
where v is speed in m/s, d is distance in m and t is time in seconds. Making d the subject of the above formula then

Substituting 343 m/s for d and 10 s for t then

Therefore, the distance between speaker and deter is 
Answer:
B
Explanation:
because it change heat with the surrounding
The energy delivered by the laser in 1 second is

In order to find how many photons correspond to this energy, we must calculate the energy of a single photon.
Calling h the Planck constant, c the speed of light and

the wavelength of the light, the energy of a single photon is given by

So, the number of photons emitted by the laser in 1 second is equal to the total energy delivered by the laser divided by the energy of a single photon:

photons
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