Question 605634
Note that {{{ h = 0 }}} at the instant the ball
is thrown upward, but also, {{{ h = 0 }}} when the ball
commes back to the surface, so:
{{{ 0 = -.8t^2 + 5t }}}
{{{ t*(-.8t + 5) = 0 }}}
The solutions are {{{ t = 0 }}} ( when ball is thrown )
and also,
{{{ -.8t + 5 = 0 }}}
{{{ .8t = 5 }}}
{{{ t = 5/.8 }}}
{{{ t = 6.25 }}}
The ball lands 6.25 sec after it is thrown