\(S_{2.5}-S_2=?\) (distance travelled in \(5^{\text {th }}\) half second)
\(S_{2.5}=u t+\frac{1}{2} a t^2\) \(a=2 \,ms ^{-2}\)
\(\Rightarrow S_{2.5}=\frac{1}{2} \times 2 \times(2.5)^2=6.25 \,m \quad(\because u=0)\)
\(S_2=\frac{1}{2} \times 2 \times 4=4 \,m\)
So, \(S_{2.5}-S_2=2.25 \,m\)