Meaning pls
1) negative terminal of power source
2) positive terminal of a power source

if you already have the answer to (a), then just work out how many periods there are in 1 minute, and that's the answer to (c).

most of them using statistics and defining how things are being measured

pretty sure it's false

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