Hang time for high speed

👨🏻‍🏫 學術台其他 - 科學

魏王將張遼

2009-12-11 8:10 am

If an object throw to the sky in a very high speed but lower than escape speed. Find the time for the object to come back to the earth surface, where x is the distance from the centre of earth to the object.

Given that at t = 0, dx/dt = u, x = R (radius of earth)

更新1:

當然係問垂直地拋, 因為橫向地拋的情況更為複雜, 而且在 7.9 km/s 或以上時, 物件是永遠不能回落地面 (在不計 air resistance 時). 題目中只寫了 "lower than escape speed", 即 11.2 km/s, 所以拋出的 speed 係有機會 >= 7.9 km/s

回答 (2)

doraemonpaul

2009-12-20 3:23 pm

✔ 最佳答案

其實類似的題目有人曾經問過，而且更是功課題：
http://hk.knowledge.yahoo.com/question/question?qid=7009031800429

2009-12-11 06:16:00 補充：
另外還有一條都算是類似的題目，不過這題似乎是興趣題：
http://hk.knowledge.yahoo.com/question/question?qid=7009031101813

2009-12-11 06:24:47 補充：
不過上述兩題你找不到是合理的，因為上述兩題確實無法取得正確的關鍵字從而找到，若不是我曾經回答，這題確實是與首個發問沒有分別。

2009-12-11 06:34:34 補充：
我亦想問清楚飛天魏國大將軍張遼：
究竟是垂直地拋，還是斜向地拋？
不過垂直地拋還是斜向地拋是否真的有分別？因為http://hk.knowledge.yahoo.com/question/question?qid=7009031800429暗示了垂直地拋都有escape velocity，而且還與橫向的完全一樣。

2009-12-11 06:57:56 補充：
ilovemadonna2009，u² - 2GM似乎是負數來的，你的回答是否很有問題？

正如，你會用ln (1 + i)來表示答案嗎？

緊記，修改已上傳的圖片是可行的，只要先把已上傳的圖片刪除，然後以同一檔案名稱重新上傳圖片，上傳完畢後按重新整理即可。這就不需要你自行移除回答，從而浪費機會。

2009-12-20 07:23:13 補充：

圖片參考：http://i212.photobucket.com/albums/cc82/doraemonpaul/yahoo_knowledge/gravitation/goodgravitation00.jpg

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參考資料：
my wisdom of physics + my wisdom of maths

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Prof. Physics

2009-12-11 9:18 am

Please refer to the following websites:

圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/ScreenHunter_01Dec110114.jpg?t=1260465446

圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/ScreenHunter_02Dec110114.jpg?t=1260465477

圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/ScreenHunter_03Dec110114.jpg?t=1260465408

http://i601.photobucket.com/albums/tt95/physicsworld9999/ScreenHunter_01Dec110114.jpg?t=1260465373

http://i601.photobucket.com/albums/tt95/physicsworld9999/ScreenHunter_02Dec110114.jpg?t=1260465393

http://i601.photobucket.com/albums/tt95/physicsworld9999/ScreenHunter_03Dec110114.jpg?t=1260465408

參考: Physics king

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收錄日期: 2021-04-19 20:50:07
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20091211000051KK00019

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