and velocity after first \(t \,sec\)

\(v = u + at\)

Now, \({S_2} = vt + \frac{1}{2}a{t^2}\)

\( = (u + at)t + \frac{1}{2}a{t^2}\)..... (ii)

Equation (ii) -(i) 

\(\Rightarrow {S_2} - {S_1} = a{t^2}\)

\( \Rightarrow a = \frac{{{S_2} - {S_1}}}{{{t^2}}} = \frac{{65 - 40}}{{{{(5)}^2}}} = 1\;m/{s^2}\)

From equation (i), we get,

\({S_1} = ut + \frac{1}{2}a{t^2}\) \( \Rightarrow 40 = 5u + \frac{1}{2} \times 1 \times 25\)

\( \Rightarrow 5u = 27.5\)

\(\therefore \;\;u = 5.5\;m/s\)