题干

如图所示,用水平拉力F拉上下表面水平、粗糙程度各处相同的物体A,使其在水平地面上匀速运动,当物体B静止不动时,与水平绳相连的弹簧测力计的示数不变。关于该状态,下列说法正确的是(不计绳和弹簧测力计重量)(  )

A:A对B的摩擦力为滑动摩擦力

B:A对B的摩擦力方向水平向左

C:弹簧测力计对B的拉力与B对A的摩擦力大小相等

D:B对A的摩擦力与水平拉力F的合力为零

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答案(点此获取答案解析)

A,C

同类题2

请认真阅读下面短文,用英语回答短文后的问题,并将答案写在横线上。


Book Review by Patricia Ann Turner

    It is school holiday time and Mitch Morrow's family have just moved to a new home in a new place. Mitch can't stop worrying about what his new school is going to be like. He  is not even sure about the neighbours. Next door live the Bull family and they have two children, Di and Bruce.  

    The older of the two,  Bruce,  is a large boy,  about Mitch's age. Mitch. Watches him carry big rocks. He looks really strong and unkind. Mitch gives him the name Bruiser(彪形大汉) because he has a black eye. Did he get it in a fight? Mitch imagines all the worst possible things about Bruiser. He is probably the class bully (恶霸). In his mind Mitch thinks of him as the enemy.

    Things seem to get more worring for Mitch. He finds out he will be in the same class as Bruiser. Then on the first day of school he learns that Bruiser is his buddy for the day.

    This is a lovely story for young readers to read or listen to. It has a wonderful message for all children about facing their fears —real and imagined.

    The pictures in the book catch the worry Mitch feels and make Bruiser rcally look like a bad guy.

    My only complaint is the colour of the printing of the text. Why there are pages of different coloured print I cannot tell. They may create problems for children with poor eyesight.

    I give it four stars.