A 75 kg mail cart traveling at 6.0 m/s to the left when it collided with Mr. Tate, who is at rest. If the mail cart comes to a complete stop, what is Terry's velocity immediately after impact?

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

answer///scientific method;