[填空题]
A cannon-ball is fired from the top of a 3nx +p/s1lcv) jpmpzpa+ -mud-cyu 25tower. The height, h, in metres, o hov4*d ue7a6rf the cannon-ball abr*e a7hd46 vuoove the ground is modelled by the function
h(t)=-2t$^2$ + 20t +8, t≥0,
where t is the time, in seconds, since the moment the cannon-ball was fired.
1.Write down the height of the tower.
h(0)= m.
2.Calculate the height of the cannon-ball 5 seconds after it was fired.
h(5)= m.
The cannon-ball hits its target on the ground n seconds after it was fired.
3.Find the value of n.
4.Find h′(t).
h'(t)=-at+b ; a=- , b= .
5.Calculate the maximum height reached by the cannon-ball, and write down the corresponding time t.
the maximum height is m and it is reached after seconds
6.Determine the total time the cannon ball was above the height of the tower.
t= seconds
