问几道初2物理寒假作业的题
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1. 设总路程st=s*(2/5)/V1+s*(3/5)/V2
v=s/t=5*V1*V2/(2*V1+3*V2)
2.有两次影子长度可达0.5m
人高度是路灯高度一般，即1：2
∴地面上影子的长度等于人离路灯的距离
∴t1=(2-0.5)/1=1.5s
t2=(2+0.5)/1=2.5s
3.36km/h=10m/s
∴t=875*2/(10+340)=5s
∴驾驶员经过5秒听到回声
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