While working out, you decide it would be funny to throw a 7.0 kg medicine ball at your friend, who is not expecting it. At the time you throw the ball towards your friend, who has a mass of 55 kg, they are walking towards you (in the opposite direction of the ball) at 0.5 m/s. If you threw the ball at 10 m/s and they reacted quickly enough to catch it, what is the combined final velocity of your friend and the ball?

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