题干

如图为四旋翼无人机,质量为1.2千克,下方悬挂着一个质量为0.1千克的摄像机。在10秒内无人机从地面竖直上升了20米,然后边摄像边斜向上飞行了30秒,仪表盘上显示离地面高度为36米。无人机前10秒对摄像机做功____焦,整个过程在,无人机对摄像机做功的功率为____瓦。


上一题 下一题 0.0难度 选择题 更新时间:2017-11-04 09:13:36

答案(点此获取答案解析)

20,0.9

同类题4

阅读理解

    Zhalong is a nature reserve in Heilongjiang in northeast China.It is one of the world's most important wetlands.The area provides food and shelter for wildlife.It is an ideal home for different kinds of plants,fish and birds.

    Many birds live comfortably in Zhalong Nature Reserve all year round,while some only stay for a short time.There are many fish in the wetlands,and the birds can easily catch them for food.Zhalong Nature Reserve is an important living area for the rare red-crowned cranes.There are not manyred-crowned cranes in the world.Some of them live in Zhalong.

    Some people want to change the wetlands to make more space for farms and buildings.This means that there will be less and less space for wildlife.

    More and more birds are in danger because they do not have enough living space.Many of them died.The Chinese government wants to protect these endangered birds,and they can be safe in Zhalong.

    Every year a lot of tourists go to Zhalong to watch birds.This year members of ourBird watching Club are going to study the different kinds of birds in Zhalongand the changes in their numbers.The study begins next month.

    We do a bird count once a year.We are now inviting secondary school students to help.We need more people to help us count and do something to help the birds.Many people do not understand the importance of the wetlands.We hope this information will help them understand and make them actively take action to protect wildlife.