Question

Define speed. What is the si unit of speed.

Answer 1

Speed=Distance÷time
the total distance covered by a vehicle upon the total time taken is called SPEED.

si unit of speed is m/s

Answer 2

The distance travelled by a body per unit time is called speed.
Speed = Distance Travelled/Time taken or
V = s / t
where v = speed 
s = distance travelled
& t = time taken
 The S.I. Unit of speed is metres per second written as m/sec .