At the Billings Auto and Highway Safety Testing Lab, a car with a crash-test dummy inside travels at 38.89 m/s (87 mi/h) toward a stationary car during a crash test. The
moving car takes 0.65 s from the point of car impact to the time when the car comes to a
complete stop. Calculate the deceleration of the car.

a.   mass number from atomic number

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