题干

我国探月工程计划之一是向月球发射月球车(如图所示)。

(1)发射月球车的火箭在穿越大气层时速度越来越快,那么,火箭受到的推力与自身重力____ (选填“相等”或“不相等”);
(2)地月之间的距离约为3.9×105千米。月球车到达月球后,如果行动指令从地球发出,到达月球车至少需要____ 秒(指令传播速度为3×105千米/秒),这样月球车的行动就不连贯了,因此我国研制智能型月球车具备独立行动能力;
(3)月球车的车轮凹凸不平,目的是为了____ (选填“增大”或“减小”)摩擦力。

上一题 下一题 0.0难度 选择题 更新时间:2018-03-10 10:01:54

答案(点此获取答案解析)

不相等,1.3,增大

同类题4

阅读理解

    Now many young people are traveling around the world on their own, not because they have no one to travel with, but because they prefer to go alone.

     Kristina Wegscheider from California first traveled alone when she was at college and believes that it is something everyone should do at least once in their life. “It opens up your mind to new things and pushes you out of your comfort zone.” Wegscheider has visited 46 countries covering all seven continents(洲).

    In foreign countries, with no one to help you read a map, look after you if you get ill, or lend you money if your wallet is stolen. It is challenging. This is what drives young people to travel alone.It is seen as character building and a chance to prove that they can make it on their own.

    Chris Richardson decided to leave his sales job in Australia to go traveling last year.He set up a website, The Aussie Nomad, to document(记录) his adventures. He said he wished he had traveled alone earlier. “The people you meet, the places you visit, or the things you do, everything is up to you and it forces you to grow as a person,” said the 30-year-old.

    Richardson describes traveling alone like “a shot in the arm”, which “makes you a more confident person that was ready to deal with anything”. He said: “The feeling of having conquered something on my own is a major part of what drives me each day when I'm dealing with a difficult task. I walk around with my head up because I know deep down inside that nothing is impossible if you try.”

    The great 19th century explorer John Muir once said: “Only by going alone in silence can one truly get into the heart of the wilderness.