Q: Can you hear the sound made by P in the shortest time when the medium is a brick wall, water, air, or vacuum?

A: The correct answer is option 'A' - brick wall.

Explanation:
When it comes to the transmission of sound waves, different mediums have different properties that affect the speed at which sound travels. In order to understand why a brick wall allows us to hear the sound made by P in the shortest time, let's look at the characteristics of each medium.

1. Brick wall:
- Sound waves are mechanical waves that require a medium to travel through. In the case of a brick wall, the sound waves can travel through the solid structure.
- Brick walls are dense and rigid, which allows sound waves to propagate quickly through them.
- The particles in the brick wall are closely packed, so the sound waves can easily transfer energy from one particle to another, resulting in fast transmission of sound.

2. Water:
- Water is a denser medium compared to air, but less dense than a brick wall.
- Sound waves can travel through water, but they propagate at a slower speed compared to in a brick wall due to the less rigid nature of water.
- The particles in water are loosely packed, so the transfer of energy from one particle to another is slower, resulting in a slower transmission of sound.

3. Air:
- Air is the most common medium through which sound waves travel in everyday scenarios.
- While air is less dense compared to water and a brick wall, it is still capable of transmitting sound.
- The particles in the air are further apart compared to those in a brick wall or water, so the transfer of energy between particles is slower, resulting in a slower speed of sound transmission.

4. Vacuum:
- A vacuum is an environment devoid of any matter, including air or any other medium.
- Since there are no particles in a vacuum, sound waves cannot propagate or travel through it.
- Therefore, sound cannot be heard in a vacuum.

In conclusion, a brick wall allows us to hear the sound made by P in the shortest time because it is a dense and rigid medium that facilitates fast transmission of sound waves.