The displacement s(t) (in metres) of a point mass moving along a line is described by
s(t)=ektcos(mt),
where k>0 and m>0 are constants and t is measured in seconds.
a. (a) Obtain general expressions for the velocity v(t) and acceleration a(t) in terms of k and m.
b. (b) Taking k=0.2 and m=3, find the smallest positive time t at which the velocity is zero.
c. (c) Using the value of t obtained in part (b), calculate the corresponding acceleration and state, with reason, whether the speed of the particle is increasing or decreasing at that instant.