The height (in metres) of a piston moving up and down in an engine cylinder after t seconds is modelled by
s(t)=5sin(4πt)+10.
(i) Obtain the velocity function v(t).
(ii) Find the velocity of the piston at t=2 s and at t=6 s.
(iii) State, with reasons, whether the piston is moving upward or downward at each of these instants.