b
Acceleration \(a=\frac{6-0}{1}=6 \,{ms}^{-2}\)

For \(t=0\) to \(t=1 \,\mathrm{s}\)

\(S_{1}=\frac{1}{2} \times 6(1)^{2}=3 \,{m}.........(i)\)

For \(t=1\) \(s\) to \(t=2 \,s\)

\(S_{2}=6.1-\frac{1}{2} \times 6(1)^{2}=3\,{m}.........(ii)\)

For \(t=2\) \(s\) to \(t=3\, s\)

\(S_{3}=0-\frac{1}{2} \times 6(1)^{2}=-3 \,{m}\)

Total displacement \(\mathrm{S}=\mathrm{S}_{1}+\mathrm{S}_{2}+\mathrm{S}_{3}=3\, \mathrm{m}\)

Average velocity \(=\frac{3}{3}=1\,{ms}^{-1}\)

Total distance travelled \(=9 \,{m}\)

Average speed \(=\frac{9}{3}=3 \,{ms}^{-1}\)