A particle of mass M originally at rest is subjected to a force whose direction is constant but magnitude varies with time according to the relation
$F=F_0\left[1-\left(\frac{t-T}{T}\right)^2\right]$
Where $\mathrm{F}_0$ nd T are constant. The force acts only for the time interval 2T. The velocity v of the particle after time 2T is :