Person standing on A will hear the loudest sound
Explanation:
The intensity of a sound wave (which is proportional to the loudness of the sound) follows an inverse square law, which is:

where
I is the intensity of the wave
r is the distance from the source of the sound
This equation means that the intensity of the sound wave (and therefore, its loudness) is inversely proportional to the square of the distance from the source: therefore,
- As we get closer to the source of sound, the loudness increases
- As we move away from the source of sound, the loudness decreases
Therefore, the person that will hear the loudest sound is the one standing closer to the source, and therefore person A.
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I don't understand that I'm sorry what grade is that
Neither energy nor matter can enter and exit an isolated system.
Explanation:
There are three types of systems which refers to universe. They are
1. Open System : In an open system, both energy and matter have external interactions. Example:- boiling water in an open pan.
2. Closed system : In a closed system, only energy has interaction with surroundings. Example:- boiling water with a lid on the pan.
3. Isolated system : In an isolated system, neither energy-nor matter has external interactions with surroundings. Example : a thermos flask does not exchange energy and matter.
Hence, the correct option is (a) " neither energy nor matter ".
Answer: It is the product of the (force)multiplied by the (perpendicular) distance from the line of action of the force to the pivot
Explanation: