The ratio of output force to the input force is generally the mechanical advantage of the machine.
The correct answer is B.
In a velocity vs time graph, a line going up means an increase in velocity, or speed, which correlates to positive acceleration. Negative acceleration means slowing down.
Wavelength = speed / frequency
(345 m/s) / (20,000 Hz) = 0.017 m
They help scientists explain concepts that are difficult to observe.