A train at a constant 60.km/h moves east for 40.0min,then in

A train at a constant 60.km/h moves east for 40.0min,then in a direction of 50.0 degree east of north for 20.0 minutes,and then west for 50.0 minutes.What are the
a) magnitude and
b) Angle of its average velocity during this trip?
翻译大概是这样?
1、一列火车以60千米/时的速度向东行驶了40分钟,然后向北偏东50度方向行驶了20分钟,然后向西行驶了50分钟.
（1）速度的大小
（2）在旅途中平均速度速度的方向

sin(40)*60*2/6=sin(40)*20 km [竖的垂直距离]
cos(40)*60*2/6=con(40)*20 kn [横的水平向东距离]
60*2/3+cos(40)*20-60*5/6=cos(40)*20-10 [横的总距离]
（(cos(40)*20-10)^2 +(sin(40)*20)^2）^(1/2)=13.92km
tanx=(sin(40)*20)/(cos(40)*20-10)
所以,x=67.55度
40+20+50=110min,
13.92/(110/60)=7.6km/h

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