A particle P has polar coordinates (r, \thetatheta). The movement of P is described as the vectorial sum of forces,

F1=-mk^{2}r
F2=-2mbv

(a) write the equations of movement
(b) suppose that the second derivative of \thetatheta is 0, determine r(t), \thetatheta(t) and thus deduce r(\thetatheta), and the speed of the particle P.