a
\(\text { Kinetic energy }(\mathrm{K})=\frac{\mathrm{P}^2}{2 \mathrm{~m}}\)

\(\Rightarrow \mathrm{P}=\sqrt{2 \mathrm{mK}}\)

\(\text { If } \mathrm{K}_{\mathrm{f}}=36 \mathrm{~K}_{\mathrm{i}}\)

\(\text { So, } \mathrm{P}_{\mathrm{f}}=6 \mathrm{P}_{\mathrm{i}}\)

\(\% \text { increase in momentum }=\frac{P_f-P_i}{P_i} \times 100 \%\)

\(=\frac{6 \mathrm{P}_{\mathrm{i}}-\mathrm{P}_{\mathrm{i}}}{\mathrm{P}_{\mathrm{i}}} \times 100 \%\)

\(=500 \%\)