如图，A、B为水平放置的平行金属板，两板相距为d，分别与电源两_爱下问搜题

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问题选择题

如图，A、B为水平放置的平行金属板，两板相距为d，分别与电源两极相连．两板的中央各有小孔M和N，今有一带电质点，自A板上方相距为d的P点由静止开始自由下落（P、M、N在同一竖直线上），空气阻力不计，到达N孔时速度恰好为零，然后沿原路径返回．若保持两极板间电压不变，则（　　）

A．若把A板向下平移一小段距离，质点自P点自由下落后将穿过N孔继续下落

B．若把B板向上平移一小段距离，质点自P点自由下落后将穿过N孔继续下落

C．若把B板向下平移一小段距离，质点自P点自由下落后将穿过N孔继续下落

D．以上说法都不正确

答案

A、由题设条件知，mg•2d-qU=0，知电场力做功等于重力做功的大小．把A板向上平移一小段距离，质点自P点自由下落，根据动能定理知，mg•2d-qU=0，小球到达N点速度为零然后返回．若将A板向下移动一小段距离，根据动能定理知，mg•2d-qU=0，小球到达N点速度也为零然后返回．故A错误．

B、C、把B板向上平移一小段距离，根据动能定理知，h＜2d，mgh-qU＜0，知小球未到达N点速度已减为零，然后返回．把B板向下平移一小段距离后，根据动能定理知，h＞2d，mgh-qU＞0，知小球到达N点速度不为零，小球会穿过N孔继续下落．故B错误．C正确．

故选C．

完形填空

The boss of an Australian restaurant is tired of the waste left by customers. He has required them to eat      on their plates or they’ll be fined and won’t be allowed to       next time.
Chef Yukako Ichikawa has introduced a 30 percent discount for customers who eat all the food they have ordered at Wafu, her      restaurant which is not far from Sydney.
"To contribute to      a future which can continue to develop, we require a little       of our guests than most other restaurants," she says and she has put up a list of her rules on the door to the restaurant .
This list includes finishing all dishes ordered which are free of milk, sugar and eggs and the cook and all her workers tell people who don't      their plates to choose       restaurant next time.
"      your meal means that everything is eaten       lemon slices, ginger(生姜) and wasabi," says the menu.
"Please also pay attention to that vegetables and salad on the      are not decorations（装饰品）; they are       of the meal too."
Wafu's strict rules have been      by some but against by some reviewers. Ichikawa insists on it.
"Wafu is not just a restaurant; it is also the      of Yukako's personal qualities ," says a statement on the restaurant's website.
“We not only serve meals and respect the body       prevent waste. We have       to protect the environment and keep the healthy development of our earth.”

B．some things

D．discovering

判断题

地球的引力是指重力。