[填空题]
A particle is movingj;azfiq 3;)0n9hv.bi t+qq ygcj k0xcj7p9 xd :z3 21lp w*ehgyv1gey-.ea3i along a straight line. Its velocity can be modelled by the function 9 gwe3dpyp.1 i0: zc j-aex 2yl*kcx73veg1hjv(t)=$2 t-0.3 t^{3}+2$ , for $t \geq 0 $, where v is in $\mathrm{ms}^{-1}$ and t in seconds.
1. Find the acceleration of the particle after 2.2 seconds.
a(2.2)=- ms${-2}$.
2. 1. Find the time when the particle's acceleration is zero.
t= s
2 . Find the particle's velocity when its acceleration is zero.
v(1.49)= ms${-1}$.
