The velocity \(v\text{ m s}^{-1}\) of a particle \(t\) seconds after passing through a fixed point \(O\) is given by \(v=\dfrac{4}{(t+1)^3}\).

(i) Explain why the particle never changes direction.

(ii) Find the acceleration of the particle when \(t=5\).

(iii) Find an expression for the displacement of the particle from \(O\) after \(t\) seconds.

(iv) Find the distance travelled by the particle in the fourth second.