[tex]Dane:\\r = 5 \ m\\f = 2 \ Hz = 2 \ s^{-1}\\Szukane:\\v = ?\\\\Rozwiazanie\\\\v = \frac{2\pi r}{T}\\\\ale \ T = \frac{1}{f}, \ zatem:\\\\v = 2\pi r f\\\\v = 2\cdot3,14\cdot5 \ m\cdot 2 \ Hz = 6,28\cdot5 \ m\cdot2 \ s^{-1}\\\\\boxed{v = 62,8\frac{m}{s}}[/tex]