[填空题]
The displacement, s , i vbnrbp(jkfd0.a)p/e5q by5 e+i re+ /n metres, of a particle t seconds after * u07ud-ad m04phwdq* t:hsy nit passes through tyd0w7 m usnq:d- h*h du*a0tp4he origin is given by the expression $s=\ln \left(1+t e^{-t}\right)$,$ t \geq 0$ .
1. Find an expression for the velocity, v , of the particle at time t .
2. Find an expression for the acceleration, a , of the particle at time t .
3. Find the acceleration of the particle at time t=0 .