The 500 kg car travelling at 25 m s-1 collides head-on with another of mass 800 kg travelling at 18 m s-1 in the opposite direction and they move together after impact. What is the magnitude of their velocity just after impact and in what direction do they move off?

the part of the wave he is travelling on is the crest

neither accurate nor precise.

i think the answer is a, hope this : )

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