A 1500 kg car traveling at 100 km/h South collides with a 1200 kg car traveling North at 100 km/h. The heavier car continues to move South after the collision, but slows to 25.0 km/h. How fast is the lighter car moving after the collision?

31.3 km/h

Explanation:

momentum before collison = momentum after collion

m1xv1 = m2xv2

25x  1500 = 1200 x v2

v2=32.25 km/h = 32.3 km/h (3 sf)

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