ii. At the point where the two graphs cross, is the speed of spacecraft A greater than, less than, or equal to the speed of spacecraft B ? Greater than Less than Equal to Justify your answer.

The answer is frictional force

Sounds propagates through some kind of medium. usually it's air, but it goes just as well through solid objects like walls, windows etc. a soundwave will compress the (air)molecules in front of it, and if this increased density wave hits your ears, you register it as sound. solid objects like walls are a lot denser than air, this means that they will damp a wave, but also carry it easier.