A small body is thrown at an angle to the horizontal with the initial velocity \(\mathbf{v}_{0}\). Neglecting the air drag, find: (a) the displacement of the body as a function of time \(\mathbf{r}(t)\) (b) the mean velocity vector \(\langle\mathrm{v}\rangle\) averaged over the first \(t\) seconds and over the total time of motion.