50% confusing

Let initial momentum be $p_0$ , final momentum be $p_1$ , mass be $m$ , initial velocity be $u$ , final velocity be $v$ , initial kinetic energy be $KE_0$ and final kinetic energy be $KE_1$ .

$p_0 = mu$

$p_1 = m v = 1.5 p_0 = 1.5 mu$

$\implies m v=1.5 m u$

$\implies v=1.5 u$

$KE_0 = \dfrac{1}{2} m u^2 = 0.5 m u^2$

$KE_1 = \dfrac{1}{2} m v^2 = \dfrac{1}{2} m (1.5u)^2 = \dfrac{1}{2} m \times2.25 u^2 = 1.125 m u^2$

Increase in $KE = \dfrac{KE_1 - KE_0}{KE_1} \times 100\%$

$\implies$ Increase in $KE = \dfrac{1.125 m u^2 -0.5 m u^2}{0.5 m u^2} \times 100\%=\dfrac{0.625 m u^2}{0.5 m u^2} \times 100\%=\dfrac{1.25 m u^2}{ m u^2} \times 100\%$

$\implies$ Increase in $KE = 1.25 \times 100\% = \textcolor{#3D99F6}{\boxed{125\%}}$