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问题 选择题

质量为1kg的滑块，以4m/s的速度在光滑的水平面上向右滑行，从某一时刻起在滑块上施加一个水平向左的2N的作用力，经过一段时间后，滑块的速度方向变为向左，大小变为6m/s，在这段时间内水平力对滑块所做的功为

A．0

B．10J

C．20J

D．26J

答案

答案：B

有动能定理，合外力做功等于动能变化量则水平力对滑块所做的功为，动能为标量与速度方向无关，B对；

问答题 简答题

絮凝的作用机理是什么？
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改错题

短文改错。

     Last summer I learnt to ride a bicycle. At first,I was unable to control it's direction. Sometimes

I fall to the right or to the left. But I asked my father to tell me how I could ride straightly. He didn't

answer me directly. Instead, he took me to side of the street. "Can you find some bike track that is

really straight?" asked my father. I watched more carefully and shook my head ."No" he said, "in fact

neither of the tracks is always straight. But just by correct the direction every now and then, you had

already gone forward."

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