A 65-kg person on in-line skates pushes against a wall, and recoils with an acceleration of 3.3 m/s2. What force does the wall exert on the person?

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

the answer is c. the lower legs are levers, and the knees are fulcrums. the ankles hold the loads.