A $1\mathrm{.}0-$kg ball having a net charge Q$=+5\mathrm{.}0$ x $10-6$ C is thrown out of a window horizontally at a speed of v$0=20$ m$/$s$.$ The window is at a height of $20$ m above ground. A uniform horizontal magnetic field of magnitude B$=0\mathrm{.}010$ T is perpendicular to the plane of the ball$$s trajectory. a$)$ Find the magnitude of the magnetic force acting on the ball just before it hits the ground. b$)$ Find the magnitude of the magnetic force acting on the ball just before it hits the ground if the ball was thrown with a speed of v$0=40$ m$/$s$.$