I lift a 20kg ball up 2.5 meters off the ground on Earth.

-Earth’s gravitational acceleration is about 9.8 m/s2.

a) How much gravitational potential energy does the ball have at this point?

b) How much work did I do lifting up the ball?

c) If I lift the same ball the same distance on the Moon, then how much gravitational potential energy will it have? (Moon’s Gravity = 1.6 m/s/s)

//(b) both involve the use of levers;

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.