Question

derive mathematically the first equation of motion v=u+at?

Answer 1

We know that
Acceleration (a) = change in velocity/time taken
                           = Final velocity (v) - Initial velocity (u) / time (t)
a = v - u/t
at = v - u
v = u + at

Hence derived

Hope this helps you.

Answer 2

Acceleration=change in velocity÷ time
a=v-u÷t
v=u+at