Choice 'D' describes speed in the metric units 'meter' and 'second'.
With no mention of direction, it can't be called 'velocity'.
<span>Pitch and frequency are more or less the same thing - high pitch = high frequency.
The freqency of vibration of a string f = 1/length (L) so as length decreases the frequency increases.</span>
The conservation of the mass of fluid through two sections (be they A1 and A2) of a conduit (pipe) or current tube establishes that the mass that enters is equal to the mass that exits. Mathematically the input flow must be the same as the output flow,

The definition of flow is given by

Where
V = Velocity
A = Area
The units of the flow of flow are cubic meters per second, that is to say that if there is a continuity, the volume of input must be the same as that of output, what changes if the sections are modified are the proportions of speed.
In this way


<span>The protons and neutrons are much more massive than the electrons.
</span>
The electrons are simply too small to really change the mass, so they aren't counted.
acceleration due to gravity is always 9.8 m/s/s (on earth)