Taking the x axis to be the original direction of motion of ball a, choose the correct equation expressing the conservation of momentum for the components in the x direction.

The answer is  a.first and third quarters 

Work is reduced while time is decreased

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.