Typical household circuits can carry a maximum current of 15 a if a wire has a resistance of a 8.0 Ω determine the voltage across the energy source

V = IR

Explanation:

I = 15 A

R = 8.0

V = 15 × 8

= 120V

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