1.
[tex]dane:\\m = 4 \ kg\\E_{p} = 80 \ J\\g = 10\frac{m}{s^{2}}\\szukane:\\h = ?\\\\Rozwiazanie\\\\E_{p} = m\cdot g\cdot h \ \ /:(m\cdot g)\\\\h = \frac{E_{p}}{m\cdot g}\\\\h =\frac{80 \ J}{4 \ kg\cdot10\frac{m}{s^{2}}} = \frac{80\frac{kg\cdot m^{2}}{s^{2}}}{40\cdot\frac{m}{s^{2}}}\\\\\underline{h = 2 \ m}[/tex]
2.
[tex]dane:\\v = 20\frac{m}{s}\\E_{k} = 20 \ kJ = 20 \ 000 \ J\\szukane:\\m = ?\\\\Rozwiazanie\\\\E_{k} = \frac{mv^{2}}{2} \ \ /\cdot2\\\\mv^{2} = 2E_{k} \ \ /:v^{2}\\\\m = \frac{2E_{k}}{v^{2}}\\\\m = \frac{2\cdot20000 \ J}{(20\frac{m}{s})^{2}}=\frac{40000 \ \frac{kg\cdot m^{2}}{s^{2}}}{400 \ \frac{m^{2}}{s^{2}}}\\\\\underline{m = 100 \ kg}[/tex]