Question

If initial velocity is 0
Kinetic energy=work done
=1/2mv^2=fxs
=ma . s
=m (v-u)/t .s
=m . v/ .s
=m.s/t/t .s
; =m s/t^2 .s
= m . s^2/t^2
= m (v)^2
= mv^2

Answer 1

When you are writing v=s/t, you are assuming that the distance s is covered at a constant speed v right from the beginning, which is wrong. Velocity is gradually increasing from 0 to v.