The ball's velocity [tex]v[/tex] at time [tex]t[/tex] is
[tex]v=v_0-gt[/tex]
where [tex]g=9.81\,\frac{\mathrm m}{\mathrm s^2}[/tex] is the acceleration due to gravity. So after 1.5 seconds, the ball's velocity is
[tex]v=64.2\,\dfrac{\mathrm m}{\mathrm s}-\left(9.81\,\dfrac{\mathrm m}{\mathrm s^2}\right)(1.5\,\mathrm s)[/tex]
[tex]\implies v=49.5\,\dfrac{\mathrm m}{\mathrm s}[/tex]
so the ball's speed after 1.5 seconds is also 49.5 m/s.
