A particle moves along a straight line and passes through a fixed point O with an initial velocity of [math]10ms^{-1}[/math]. The acceleration, a [math]ms^{-2}[/math], at t seconds after passing through O is given by [math]a=4t-8[/math]
(a) the instantaneous velocity, in [math]ms^{-1}[/math] , of the particle at the 4th second.
(b) the minimum velocity, in [math]ms^{-1}[/math] , of the particle