Initial kinetic energy \(=\frac{p_1^2}{2 m }\)

Final kinetic energy \(=\frac{p_f^2}{2 m }=\frac{\left(1.5 p _{ i }\right)^2}{2 m }\)

\(=\frac{2.25 p _{ i }^2}{2 m }\)

\(\%\) increase in \(KE =\frac{2.25 \frac{ p _{ i }^2}{2 m }-\frac{ p _{ i }^2}{2 m }}{\frac{ p _{ i }^2}{2 m }} \times 100=125 \%\)