There is another aspect of flying we must now know about,that is flying speeds.There are,in fact,tow

题目

There is another aspect of flying we must now know about,that is flying speeds.There are,in fact,tow kinds of speed:the ground speed,which is the actual speed of the plane in relation to the ground,and the air speed,which is the speed relative to the air.These are two quite different things.
Let us go back to the kite for a moment.If,in still air,you run with a kite at five miles per hour,its ground speed will be five miles per hour because that is the actual speed at which you are pulling it over the ground.Now,suppose you are running at five miles per hour.The ground speed will still be the same but,because the air is passing the kite at ten miles per hour,the air speed of the kite will be ten miles per hour; that is ,the speed at which you are running plus the speed of the air blowing past the kite.Stand still with your kite in the same breeze.Its ground speed is now nothing,but the air is passing the kite at five miles per hour,so its air seed is five miles per hour.
Ground

答案

36 C
37 C
38 D
39 C
40 A
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