A) a block of mass, m, is pushed up against a spring, compressing it a distance x, and is then released. the spring projects the block along a frictionless horizontal surface, giving the block a speed v. the same spring projects a second block of mass 4m, giving it a speed 3v. what distance was the spring compressed in the second case?
b) initially a body moves in one direction and has kinetic energy k. then it moves in the opposite direction with three times its initial speed. what is the kinetic energy now?

a)

KE=1/2mv^2

F= -kx

KE= -kx

-kx= 1/2mv^2

when u quadruple the m, the x also quadruples. when the speed is multiplied by 3, since it is v^2, the x is multiplied by 3^2 , which is 9

so distance the spring compressed is x×4×9= 36x

b) using the KE formular too,

when the v is tripled, since formula is v^2, the resulting KE will be multiplied by 3^2, so KE now= 9K

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