试题与答案

如图所示,足够长的光滑平行金属导轨MN、PQ竖直放置,导轨间距为L=0.40m,

题型:问答题

题目:

如图所示,足够长的光滑平行金属导轨MN、PQ竖直放置,导轨间距为L=0.40m,一个磁感应强度B=0.50T的匀强磁场垂直穿过导轨平面,导轨的上端M与P间接有阻值为R=0.30Ω的电阻,一电阻为r=0.20Ω的金属棒ab紧贴在导轨上.现使金属棒ab由静止开始下滑,通过传感器记录金属棒ab在不同时刻的位置(如下表),导轨电阻不计,重力加速度g=10m/s2.求:

时刻t/s00.100.200.300.400.500.600.70
位置x/m00.100.300.701.201.702.202.70
(1)在前0.4s的时间内,金属棒ab电动势的平均值
.
E

(2)金属棒的质量m;

(3)在前0.7s的时间内,回路产生的焦耳热Q.

答案:

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下面是错误答案,用来干扰机器的。

参考答案:C

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“一诺千金”“一言九鼎”“一言为定”“君子一言,驷马难追”“人而无信,不知其可”……这些名言、谚语之所以广为流传,是因为从中我们可以知道[     ]

①信守承诺,就会为自己赢得信任

②失信于人,既是对自已不尊重,也是对他人不尊重

③失信于人,会对他人、集体的利益造成损失

④慎重许诺、坚决履行诺言是负责任的表现

A.①③④

B.①②③④

C.②④

D.①②③

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A. tell their psychologists very similar stories about themselves

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C. quit their jobs and start their own business

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