1.一艘轮船以20km/h的速度顺流而下由甲地到达乙地,又以10km/h的速度逆流而上由乙地返回甲地,求轮般在甲,乙两地往返中的平均速度是多少?
2019-06-21
1.一艘轮船以20km/h的速度顺流而下由甲地到达乙地,又以10km/h的速度逆流而上由乙地返回甲地,求轮般在甲,乙两地往返中的平均速度是多少?
优质解答
设两地的距离为S
则有:
V平均=2S/t总
=2S/(t1+t2)
=2S/(S/v1+S/v2)
=2S/(Sv2/v1v2+Sv1/v1v2)
=2S/[(Sv2+Sv1)/v1v2
=2S*v1v2/S(v1+v2)
=2v1v2/(v1+v2)
=2*20*10/(10+20)
=400/30
=13.34km/h
设两地的距离为S
则有:
V平均=2S/t总
=2S/(t1+t2)
=2S/(S/v1+S/v2)
=2S/(Sv2/v1v2+Sv1/v1v2)
=2S/[(Sv2+Sv1)/v1v2
=2S*v1v2/S(v1+v2)
=2v1v2/(v1+v2)
=2*20*10/(10+20)
=400/30
=13.34km/h