E_{mech}=E_k+E_P
E_{m1}=E_{m2}
{E_{k1}+E_{p1}=E_{k2}+E_{p2}
\frac{m{v_1}^2}{2}+mgh=\frac{m{v_2}^2}{2}+mgH |:m
\frac{{v_1}^2}{2}+gh=\frac{{v_2}^2}{2}+gH |*2
{v_1}^2+2gh={v_2}^2+2gH
{v_1}^2+2gh-2gH={v_2}^2
{v_1}^2+2g(h-H)={v_2}^2
podstawiam dane
(4\frac{m}{s})^2+2*10\frac{m}{s^2}(2,6m-3,05m)={v_2}^2
16\frac{m^2}{s^2}+20\frac{m}{s^2}*(-0,45m)={v_2}^2
16\frac{m}{s^2}-9\frac{m^2}{s^2}={v_2}^2
{v_2}^2=7\frac{m}{s^2}
v_2=\sqrt{7\frac{m^2}{s^2}}\approx2,65\frac{m}{s} <-- odpowiedź