[填空题]
$\text { A particle moves in a straight line such that its velocity, } v \mathrm{~m} \mathrm{~s}^{-1} \text {, at time } t \text { seconds, is given by }$
1. Find the value of t , for t>0 , when the particle is instantaneously at rest.
The particle returns to its initial position at t=T .
2. Find the value of T . Give your answer correct to three significant figures. ≈
