Let m be the mass of the body and v₁ and v₂ be the initial and final velocities of the body respectively.

$\therefore$ Initial kinetic energy = ${1 \over 2}mv_1^2$

Final kinetic energy = ${1 \over 2}mv_2^2$

Initial kinetic energy is increased 300% to get the final kinetic energy.

$\therefore$ ${1 \over 2}mv_2^2 = {1 \over 2}\left( {1 + {{300} \over {100}}} \right)mv_1^2$

$\Rightarrow$ v₂ = 2v₁ or v₂/v₁ = 2 ... (i)

Initial momentum = p₁ = mv₁

Final momentum = p₂ = mv₂

\therefore $$${{{p_2}} \over {{p_1}}} = {{m{v_2}} \over {m{v_1}}} = {{{v_2}} \over {{v_1}}} = 2$$<br><br> \therefore $ ${p_2} = 2{p_1} = \left( {1 + {{100} \over {100}}} \right){p_1}$

So momentum has increased 100%.