Answer:
about 42.35 m/s
Explanation:
Use the equation for accelerated motion (g), and with zero initial velocity that doesn't include time:

which for our case would reduce to:

then the velocity just before hitting would be about 42.35 m/s
Answer a) is incorrect as sound does not travel in a vacuum.
B) a rock being tossed high into the air
There are many factors which contributes as to how a machine will be processing the input energy and convert it to output energy. Even with identical mechanism, these factors will have major effect on the output. Some factors are deflection, friction and wear. Some system maybe exposed to poor lubrication than the other which'll produce more friction and wear thus lower mechanical advantage.