## College Physics (7th Edition)

$4.9t^{2}-30t+10=0$ 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