Answer
a) $J=407kg\frac{m}{s}$
b) $=1.5\times10^5N $ upward
c) $=3.6\times10^3N$ upward
Work Step by Step
a) $J=\Delta p$
$v_f=\sqrt{2gh}=\sqrt{2(9.8\frac{m}{s^2})(2.8m)}=7.4\frac{m}{s}$
$J=m(v_f-v_i)=(55kg)(7.4\frac{m}{s})=407kg\frac{m}{s}$
b) $\sum F=F_g-mg=ma$
$F_G=m(g+a)=m(g+\frac{v_f^2-v_i^2}{2\Delta x})$
$=(55kg)\Big((9.8\frac{m}{s^2})+\frac{(7.4\frac{m}{s})^2-(0\frac{m}{s})^2}{2\times 2.81m}\Big)$
$=1.5\times10^5N $upward
c) $F_G=(55kg)\Big((9.8\frac{m}{s^2})+\frac{(7.4\frac{m}{s})^2-(0\frac{m}{s})^2}{2\times 3.30m}\Big)$
$=3.6\times10^3N $upward
This is why it is less painful and safer when you bend your knees when you land after jumping or falling.