[填空题]
The following diagram shows a ball attached to the end of a-1id zxw xr :,h)apq2x sprisfhllkx,nl 5(. q 5xf 9zi*yc4ng, which is suspl*ckyxh l(i5s4n, l.9z5 ffxqended from a ceiling.
The height, h metres of the ball above the ground at time t seconds after being released can be modelled by the function h(t)=0.5 $\cos (\pi t)+2.2$, where $t \geq 0 $.
1. Find the height of the ball above the ground when it is released.
2. Find the minimum height of the ball above the ground.
3. Show that the ball takes 2 seconds to return to its initial height above the ground for the first time.
4. For the first 2 seconds of its motion, determine the amount of the time that the ball is less than $2.2+0.25 \sqrt{2}$ meters above the ground.
5. Find the rate of change of the ball's height above the ground when $t=\frac{1}{3}$ . Give your answer in the form p $\pi \sqrt{q} \mathrm{~ms}^{-1} $, where $p \in \mathbb{Q}$ and $q \in \mathbb{Z}^{+}$ $\mathrm{ms}^{-1}$
