题干

如图,位于A处的海上救援中心获悉:在其北偏东68°方向的B处有一艘渔船遇险,在原地等待营救.该中心立即把消息告知在其北偏东30°相距20海里的C处救生船,并通知救生船,遇险船在它的正东方向B处,现救生船沿着航线CB前往B处救援,若救生船的速度为20海里/时,请问:救生船到达B处大约需要多长时间?(结果精确到0.1小时:参考数据:sin38°≈0.62,cos38°≈0.79,sin22°≈0.37,cos22°≈0.93,sin37°≈0.60,cos37°≈0.80)

上一题 下一题 0.0难度 选择题 更新时间:2018-03-11 08:56:36

答案(点此获取答案解析)

解:如图,延长BC交AN于点D,则BC⊥AN于D.
在Rt△ACD中,∵∠ADC=90°,∠DAC=30°,
∴CD=
1
2
AC=10,AD=3

同类题1

阅读理解

A Book Review—The Snake-Stone by Berlie Doherty

    The setting: Urban England (the cities), but also rural England (the countryside) including remote English villages.

    The theme: The main theme is a teenage search of self-discovery, in this case the search for a mother from whom the hero was separated at an early age. Its other concerns are love, getting on with others, being persistent and courageous and trying to deal with doubts, troubles and worries. As the book moves to a close, James' swimming coach says to him: “You are not like a kid obeying instructions any more. You are diving like a young man who knows where he is going.”

    The characters: James is the hero of the story. He is a championship diver, and has a comfortable life with his foster parents (养父母). Yet he also has the qualities to take him on a long journey to find his birth mother. The other characters in The Snake-Stone, James' parents, his diving instructor, best friend, the villagers, people he meets on his journey, are pictured realistically.

    The turning point: The turning point in the story comes while James' foster parents are away in London, and he wonders about the identity of his birth mother. The only clue he has is a fossil, “the snake stone” which she left behind along with a note on which she had written: “Take good care of Sammie. It was written on a torn envelope with parts of an address still there.

    The journey: Instead of going to London, James decides to find his birth mother. With help from his geography teacher, James sets out for the remote country village where his mother might be found. James has painful, challenging, but also humorous and happy travels. The mother he finally meets, Anne, has a minor yet powerful voice in the novel. He comes to understand why she left him at a stranger's door fifteen years before. Although the meeting is not long, it leaves him with a feeling of completeness. As a journey of self-discovery The Snake-Stone also provides its readers with a happy ending. Its hero says, on returning to his foster parents, “I was home.”