Which is the best analogy of a wave? a. a wave is like building a ramp. b. a wave is like shaking a hand. c. a wave is like water rippling in a pond. d. a wave is like knocking down a building.

C. A wave is like water rippling in a pond.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.