试题与答案

如图所示,足够长的两根光滑导轨相距0.5m竖直平行放置,导轨电阻不计,下端连接阻

题型:问答题

题目:

如图所示,足够长的两根光滑导轨相距0.5m竖直平行放置,导轨电阻不计,下端连接阻值为1Ω的电阻R,导轨处在匀强磁场B中,磁场的方向垂直于导轨平面向里,磁感应强度为0.8T.两根质量均为0.04kg、电阻均为0.5Ω的水平金属棒ab、cd都与导轨接触良好,金属棒a6用一根细绳悬挂,细绳允许承受的最大拉力为0.64N.现让cd棒从静止开始落下,直至细绳刚好被拉断,在此过程中电阻R上产生的热量为0.2J,g取10m/s2,求:

(1)此过程中ab棒和cd棒分别产生的热量Qab和Qcd;

(2)细绳刚被拉断时,cd棒的速度;

(3)细绳刚被拉断时,cd棒下落的高度.

(4)cd棒从静止开始落下直至细绳刚好被拉断所经过的时间.

答案:

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Nearly a quarter-century after a German boy threw a message in a bottle off a ship in the Baltic Sea, he’s received an answer.

A 13-year-old Russian, Daniil Korotkikh, was walking with his parents on a beach when he saw something lying in the sand.

“I saw that bottle and it looked interesting,” Korotkikh told The Associated Press on Tuesday. “it looked like a German beer bottle and there was a message inside. ”

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The boy in the letter, Frank Uesbeck, is now 29. His parents still live at the letter’s address.

The Russian boy and the German man met each other earlier this month through an internet video link. The Russian boy said he did not believe that the bottle actually spent 24 years in the sea. He believed it had been hidden under the sand where he found it for a long time.

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B.The German boy did not believe that the bottle actually spent 24 years in the sea.

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A.Because he could have a new friend.

B.Because the two boys could surf the internet together.

C.Because he could have a positive influence on a life of a young person.

D.Because he finally got what he had lost.

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