Many medical techniques rely on ultrasonic waves. True or false

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.

it is a negative acceleration

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