a simple pendulum of length L is set to oscillate in simple motion .The bob gravitational potential energy is zero at its lowest vertical point . When the bob's height is at half its maximum h=hmax/2 then its velocity is?

The answer is that they are composed mostly of liquid water.

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.