题干

如图甲所示,一块长木板放在水平桌面上,现用一水平力F1向右缓慢地推木板,使其一部分露出桌面,如图乙所示,在推木板的过程中木板对桌面的压力F、压强p和摩擦力f的变化情况是(  )

A:Fp不变,f变大

B:Ff不变,p变大

C:F变小,pf变大

D:Ff不变,p变小

上一题 下一题 0.0难度 选择题 更新时间:2019-03-31 09:47:07

答案(点此获取答案解析)

B

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    The Van Gogh Museum in Amsterdam has welcomed home two paintings by the Dutch master, more than 14 years after they were ripped (抢) off the museum's wall in a nighttime theft. Museum director Axel Rueger called their return “one of the most special days in the history of the museum.”

    The paintings were discovered last year by Italian police while they were searching suspected Italian criminals' farmhouse near Naples for evidence of drug dealing. The two paintings were wrapped in cotton sheets. They were stuffed in a box and hidden behind a wall in a toilet when they were found.

    The paintings were considered among the artworks most searched for in the world. After years in darkness, they can now shine again. They are back on display at the museum before being taken to the conservation studio for repair. Fortunately, they suffered remarkably little damage as thieves who had climbed up a ladder and broken a window to get into the museum in 2004 rip them out of their frames.

    “It is not only a surprise that the works have been recovered but it's even more surprising they are in relatively unharmed condition,” Rueger said.

    The museum director was on vacation when the call came last year from Italian authorities who believed they had recovered the paintings. He didn't celebrate right away. He'd had calls like this before.

    “I was hopeful but also a little hesitant. Over these years, we had so many occasions when people phoned us, contacted us, claiming that they knew something about the whereabouts (下落) of the works and each time it was false, the trace went cold,” he said. “So...the way has been till of disappointment.” But museum experts sent to Italy to check the authenticity(真实性) of the works quickly turned Rueger's doubts into delight.

    Rueger said the paintings are now back permanently at the museum, which is home to dozens of works by Van Gogh. “I'm very confident that everything is safe in the museum from now on,” he said.