Using the equation of motion

s = ut + at 1/ 2 at^{2}

Distance travelled in 5 s s = u × 5 +1/2 a × 5^{2}

or s = 5 u + 25/ 2 a ——(i)

Similarly, distance travelled in 4 s, s′ = 4 u + 16/ 2 a——(ii)

Distance travelled in the interval between 4^{th} and 5^{th} second

= (s – s′) = (u +9/2 a) m