3.
[tex]Dane:\\m = 20 \ kg\\v = 36\frac{km}{h} =36:3,6\frac{m}{s}=10\frac{m}{s}\\Szukane:\\E_{k} = ?\\\\Rozwiazanie\\\\E_{k} = \frac{1}{2}at^{2}\\\\E_{k} = \frac{1}{2}\cdot20 \ kg\cdot(10\frac{m}{s})^{2}\\\\\boxed{E_{k} = 1000 \ J = 1 \ kJ}[/tex]
4.
[tex]Dane:\\v_{o} = 72\frac{km}{h} = 72:3,6\frac{m}{s} = 20\frac{m}{s}\\h = 5 \ m\\g = 10\frac{m}{s^{2}}\\Szukane:\\v = ?\\\\Rozwiazanie\\\\E_{k} = E_{k_{o}}-E_{p}\\\\\frac{mv^{2}}{2}=\frac{mv_{o}^{2}}{2} - mgh \ \ /\cdot\frac{2}{m}\\\\v^{2}-v_{o}^{2} -2gh\\\\v = \sqrt{v_{o}^{2}-2gh}}[/tex]
[tex]v = \sqrt{(20\frac{m}{s})^{2}-2\cdot10\frac{m}{s^{2}}\cdot5 \ m}}} =\sqrt{(400-100)\frac{m^{2}}{s^{2}}} = \sqrt{300\frac{m^{2}}{s^{2}}}\\\\\boxed{v \approx17,32\frac{m}{s}}[/tex]
