I need some help with this question, pls and thank you!! An object cannot have:
a) a velocity vector and an acceleration in the same direction.
b) a velocity vector and an acceleration in opposite directions.
c) a constant velocity vector and a variable acceleration.
d) constant acceleration and a variable speed vector

i don't know that i agree with that but what's the question ?

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on 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