The equation of motion is given for a particle by $s(t)=2t^3-7t^2+4t+ 3$ where $s$ is in meters, and $t$ is in seconds. Find:
(a) The velocity function.
(b) The acceleration function.
(c) The acceleration at the first (positive) instant when the velocity is zero.

(a) $v(t) =$
(b) $a(t) =$
(c) accel. $=$ $m/s^2$