A man unloads a 4.0-kg box from a moving van by giving it an initial speed of 1.1 m/s down a ramp that makes an angle of 18° with the horizontal. It slides with negligible friction for 2.3 m along the ramp before reaching the man's helper. What is the speed of the box as the helper catches it?

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