Define speed. What is its S.I. unit ?

Speed of a body is the rate of change of distance with time .

It is a scalar quantity. It is generally represented by u or v .

If a body travels a distance S in time t, then its speed v is —

$\text{Speed (v)} = \dfrac{\text{Distance (S)}}{\text{Time (t)}} = \dfrac{\text{S}}{\text{t}} \\[0.5em]$

$\text{S.I. unit of speed} = \dfrac{\text{metre}}{\text{second}} = \dfrac{\text{m}}{\text{s}} \\[0.5em] \text{C.G.S. unit of speed} = \dfrac{\text{centimetre}}{\text{second}} = \dfrac{\text{cm}}{\text{s}} \\[0.5em]$.