[填空题]
The displacement, s , in metres, o why+rd4 *g ed7etuszl5(x1*zf a particle t secoo18wuc)b+ kfs2 t j,rakjep,e 1 0ux9hnds after it passes through the orpe9jo1sx,kjr )ac t+2 h 0euw k1bu8f,igin 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 .