Answer
There are 2 physically reasonable roots i.e. 0.35s and 5.8s
Work Step by Step
$4.9t^{2}-30t+10=0$
As roots of the equation,
$t=\frac{30+/-\sqrt (30^{2}-4\times4.9\times10)}{2\times4.9}$
$t=\frac{30+/-26.53}{9.8}=0.35s\,\,\, or \,\,\,5.8s$
So, there are 2 physically reasonable roots i.e. 0.35s and 5.8s
