如图甲所示，平行于光滑斜面的轻弹簧劲度系数为k，一端固定在倾角为θ的斜面底端，另一端与物块A相连．两物块A、B质量均为m，初始时均静止．现用平行于斜面向上的力F拉动物块B，使B做加速度为a的匀加速运动

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如图甲所示，平行于光滑斜面的轻弹簧劲度系数为k，一端固定在倾角为θ的斜面底端，另一端与物块A相连．两物块A、B质量均为m，初始时均静止．现用平行于斜面向上的力F拉动物块B，使B做加速度为a的匀加速运动，A、B两物块在开始一段时间内的v﹣t关系分别对应图乙中的A、B图线（t₁时刻A、B的图线相切，t₂时刻对应A图线的最高点），重力加速度为g，则（　　）

A：t₂时刻，弹簧处于原长状态

B：t₁时刻，弹簧型变量为 $\frac{m g s i n θ + m a}{k}$

C：从开始到t₂时刻，拉力F逐渐增大

D：t=0时刻，拉力满足F=2ma

上一题下一题 0.0难度选择题更新时间:2020-03-08 12:11:25

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B,D

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文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。

增加：在缺词处加一个漏字符号(∧)，并在其下面写出该加的词。

删除：把多余的词用斜线(\)划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词

2）只允许修改10处，多者（从第11处起）不计分。

A man requested on a wise man to help his son quit his bad habits. The wise man took the boy for walk in a garden. Suddenly he stopped to ask the boy to pull out a tiny plant there. The boy hold the plant between his thumb and forefingers and pulled it out. The man then asked him to pull out another plant what was a little big. The boy pulled hardly and the plant came out. “Now pull out that one,” said the man point to a bush. The boy tried his best but couldn't pull it out. “So it is the same with bad habits” said the wise man. “When you are weak, it is easy to pull them out, though when they become strong, they can't be rooted.”

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