Of 18.0 m, 1140 J of mechanical energy are dissipated. Another 1720 J of mechanical energy are
dissipated while moving from location B to C. Determine the missing potential
energy (PE) and kinetic energy (KE) values for locations A, B, and C and calculate
the speed at C. Use g = 9.8 N/kg

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