A car, starting from rest, accelerates at the rate $\alpha$ through a distance $d$, then continues at a constant speed for time $t$ and then decelerates at the rate of $\alpha/2$ to come to rest. If the total distance traveled is $15\, d$, then $d=$
$d = \frac{1}{2}\, \alpha \, t^2$
$d = \frac{1}{4}\, \alpha \, t^2$
$d = \frac{1}{72}\, \alpha \, t^2$
$d = \frac{1}{6}\, \alpha \, t^2$
A bullet fired into a fixed target loses half of its velocity after penetrating $3\, cm$. How much further it will penetrate before coming to rest assuming that it faces constant resistance to motion ?.......$cm$
The same retarding force is applied to stop a train. The train stops after $80\, m$. If the speed is doubled, then the stopping distance will be