$4.(7\mathrm{.}5)$ A tennis ball is thrown from the roof of a $20\mathrm{.}8-$m$-$tall building with an initial velocity of magnitude $11\mathrm{.}5$ m$/$s and directed at an angle of $50\mathrm{.}1$above the horizontal. a$.$ What is the speed of the ball just before it strikes the ground? Use energy methods and ignore air resistance. b$.$ What is the answer for part $($a$)$ if the initial velocity is at an angle of $50\mathrm{.}1$ below the horizontal? c$.$ If the effects of air resistance are included, will part $($a$)$ or $($b$)$ give the higher speed?