you are holding a block (mass m) just above a spring (constant k) that is sitting vertically on the floor. You slowly lower the block on to the spring, until you no longer need to support it to prevent it from falling.. What is the maximum distance that it compresses the spring

the answer would be a

d. platinum would have the greatest temperature increase because it has the lowest specific heat.

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