Answer
a). $a=-1.78m/s^{2}$
b). $t=6.275s$
Work Step by Step
a). $25mi/hr = 25\times \frac{1609 m}{3600 s}=11.17m/s$
$v^{2}=u^{2}+2aS$
$0=11.17^{2}+70a$
i.e. $a=-1.78m/s^{2}$
b). $v=u+at$
$0=11.17-1.78\times t$
$t=6.275s$
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