[填空题]
The displacement, s , in metres, o dgrnzmzck:.7h-x*kq 729lm lf a particle 6 rv1oz:wh.f j t seconds after it passes through f:o6.jwzhv1 r the 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 .