Length is a fundamental quatity. But area is a derived one.
Because area is nothing but the product of length and length.
Volume too is a derived one as volume is length x length x
length.
Mass in fundamental. But density is mass / volume. Hence density
is derived. Density is mass / lengthx lengthx length
Same way time is fundamental . BUt speed is derived as speed is
distance ie length divided by time. So speed is length/ time.
Electric current is fundamental. But electric charge is a
derived one as charge = current x time.
Work done is derived as work is got right from mass x length x
length / time x time.
Why so? Force x distance gives work. Mass x acceleration =
force.
But acceleration = velocity/ time. In turn velocity = length /
time.
So acceleration is length / time x time
Hence force mass x length / time x time
THere by work mass x length x length / time x time.