v人=2v梯链袭,设总距离为S1.t(人+梯)=S/(v人+v梯)=S/3v梯,由题知S/v梯 = 120秒,所以t(人+梯)备唤蠢=120/3 =40s2.t(人-梯)=S/(v人-v梯)=S/v梯仿陪,所以t(人-梯)=2min,即120s
40 1201/闷坦60+1/120=拍罩罩1/401/60-袭闹1/120=1/120
40120