Khi thang máy đứng yên:$\triangle L=\frac{mg}{k}=\frac{0,4.10}{25}=16(cm)$Ta có:$A=\frac{l max-l min}{2}=\frac{48-32}{2}=8(cm)$
$\Rightarrow l bđ=l max-\triangle L-A=24(cm)$
Khi thang máy đi lên:$ \triangle L1=\frac{m(a+g)}{k}=19,2(cm)$
Khi đó:$A'=A-\triangle L1+\triangle L=4,8(cm)$
$\Rightarrow l max=l bđ+\triangle L1+A'=48(cm)$
$l min=l max-2A'=38,4(cm)$