$\begin{array}{l}
According\,to\,question,\,{u_1} = 40\,km/h,\,{v_1} = 0\\
and\,{s_1} = 40\,m\\
{\rm{using}}\,{{\rm{v}}^2} – {u^2} = 2as;\,{0^2} – {40^2} = 2a \times 40\,\,\,\,\,\,…\left( i \right)\\
Again,\,{0^2} – {80^2} = 2as\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,…\left( {ii} \right)\\
From\,eqn.\left( i \right)\,and\,\left( {ii} \right)\,\\
Stopping\,{\rm{ distance}},\,s = 160\,m\,\,
\end{array}$