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【简答题】
某实验小组的同学采用如图所示的装置(实验中,小车碰到制动装置时,钩码尚未到达地 面)来 “ 探究恒力做功与动能改变的关系 ” 。图 10是实验中得到的一条纸带,点 O 为纸带上的起始点, A 、 B 、 C 、 D 、 E 是纸带上的五个连续的计数点,相邻两个计数点间均有4个点未画出,用刻度尺测得五个点到 O 的距离如图10所示。已知所用交变电源的频率为50 Hz,则: (1)开始实验时首先应______________________________________。 (2)打 B 、 D 两点时小车的速度分别为 v B = ________m/s, v D = ________m/s。 (3)若钩码的质量 m = 250 g,小车的质量 M = 1 kg,则从 B 至 D 的过程中,根据实验数据计算的合力对小车做的功 W = ________J,小车动能的变化Δ E k = ________ J。(结果保留两位有效数字) (4)由实验数据,他们发现合外力做的功与小车动能的变化有一定的偏差,产生误差的原因可能是________________ ________ 。 (至少说出一条)
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A.
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B.
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C.
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A.
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the
【单选题】I've been a student there for nearly two and _______ half years.
A.
a
B.
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D.
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