An object moves along a line so that its position s relative to a starting point at any time $t \geqslant 0$ is given by $s(t)=\cos \left(t^{2}-1\right)$
a) Find the velocity of the object as a function of $t$
b) What is the object's velocity at $t=0 ?$
c) In the interval $0 < t < 2.5,$ find any times (values of $t$ ) for which the object is stationary.
d) Describe the object's motion during the interval $0 < t < 2.5$