如图所示，在水平面上有一质量为M的长木板，开始时长木板上有一_爱下问搜题

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问题计算题

如图所示，在水平面上有一质量为M的长木板，开始时长木板上有一质量为m的小铁块（视为质点）以相对地面的大小为V₀的初速度从长木板的中点沿长木板向左滑动，同时长木板在沿水平向右的拉力F作用下始终以大小为V的速度作匀速运动（V ＞V₀），小铁块最终跟长木板一起向右做匀速运动。已知小铁块与木板，木板与水平面间的摩擦因数均为μ，试问：

（1）小铁块从中点开始运动到最终匀速运动过程中水平拉力F的大小为多少？

（2）长木板至少为多长？

答案

解：（1）如图M的匀速运动时有

F=μ·（M＋m）g＋μ·mg

F=" " μ·（M＋2m）g

（2）设木板长为L，m滑行加速度大小为a，则a=

≥v·t－

t=

联立得L≥

填空题

Blair Admits Never Having Sent Flowers to His Wife

British Prime Minister Tony Blair admitted on a television programme that he has never sent flowers to his wife Cherie and that he had a youthful crush on Hollywood beauty Grace Kelly.
Blair, who allowed Channel 4 interviewer June Sarpong to shadow him for two days last month, made other personal (1) when asked questions he rarely hears on the usual television political (2) .
During the interviews for a program targeting 18-30 year (3) , the prime minister admitted he sometimes has to "wing it" when (4) public appearances and that he yearns to go out for a drink (5) being recognised.
However, the most dramatic revelation was his reply to Sarpong’s (6) on whether he still sends his wife flowers, prompting his interviewer to (7) in disbelief. "I’ve never sent her flowers. If I sent her flowers, she would (8) worried," Blair said.
But he added: "I am romantic. There are other ways of (9) romantic."
Blair needed a few moments to recall which posters he had (10) his bedroom wall as a youngster, then revealed: "I’ll tell you... actually, (11) I was younger, I loved Grace Kelly."
Born in 1929, Kelly (12) in films like ’Dial M For Murder’, ’Rear Window’ and ’High Society’ in the mid-1950s, but (13) acting to marry Prince Rainier of Monaco in 1956, when Blair was (14) two years old.
Blair admitted he initially found it "odd" to be (15) minister and to be rushed in motorcades from appointment to (16) , and worried that his lifesty left him "a bit isolated" from (17) people.
He admitted that he was constantly on the phone between public (18) , and rarely had time to prepare for his next (19) , telling Sarpong: "I wing it all the time."
And he revealed he has to check himself before he replies to (20) questions from the public. "The worst thing is when someone is giving you a real earful and you think ’I’m going to say something I will regret’," he said.
Asked what he would do if he could be invisible for a day, Blair yearned for a more ordinary life, saying he would "just walk down the street and go to the pub... just be absolutely normal".

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