题干

如图,身高1.6米的小明从距路灯的底部(点O)20米的点A沿AO方向行走14米到点C处,小明在A处,头顶B在路灯投影下形成的影子在M处.

(1)已知灯杆垂直于路面,试标出路灯P的位置和小明在C处,头顶D在路灯投影下形成的影子N的位置.

(2)若路灯(点P)距地面8米,小明从A到C时,身影的长度是变长了还是变短了?变长或变短了多少米?

 

上一题 下一题 0.0难度 选择题 更新时间:2019-02-02 06:16:36

答案(点此获取答案解析)

解:(1)如图

(2)设在A处时影长AM为x米,在C处时影长CN为y米

同类题2

 Many people believe that yellowing and wetness are the greatest enemy of stamps. In fact, stamps are afraid of not only wetness, but also light and dirty things. People protect their stamps in several different ways.

 To protect stamps,we should never touch the stamps with our hands.This avoids moving dirty things onto them. Stamp tweezers (镊子) should be used in all conditions.

 Stamps are printed things. The colour will slowly disappear if the stamps are put in the light for a long time. So we should not put stamps in the light for long. Direct sunlight must be avoided as well.

 Wetness is an important  problem for stamps. Some  collectors  will put stamps  in separate plastic (塑料) bags. However, it is possible that some stamps have taken in some water from the air before they are put into the plastic bags.Stamps yellow easily and rapidly after they take in wet air.To protect the stamps, some people also put the stamps into a special room which has a machine to  keep the air cool and dry. However, not many people can afford that.

 To keep stamps, stamp collectors usually put them under plastic covers. It is a common and simple way. This helps because the plastic cover keeps the stamps off the wet air. It also stops the fingersfrom touching te stamps.

 Some  collectors  prefer  to  store  stamps  inside  a  plastic  box  with  desiccants  (干燥剂).However, we should take care not to let the stamps. touch the desiccants. On top of that, don't  take your stamps out on a wet day.