[填空题]
Note: In this question, distance is in metrtuu;+uu: + drles and time ist(t5 5 :3 yxhut5fomauct-p(d in seconds.
A particle P moves in a straight line for six seconds. Its acceleration during this period is given by $a(t)=-2 t^{2}+13 t-15 $, for $0 \leq t \leq 6$ .
1. Write down the values of t when the particle's acceleration is zero.
2. Hence or otherwise, find all possible values of t for which the velocity of P is increasing.$a\lt t \lt b$ a = b =
The particle has an initial velocity of 7 $\mathrm{~ms}^{-1}$ .
3. Find an expression for the velocity of P at time t .
4. Find the total distance travelled by P when its velocity is decreasing.
