试题与答案

如图所示,站在汽车上的人用手推车,车对手的力为F,车对脚的静摩擦力为F′,下列说

题型:不定项选择

题目:

如图所示,站在汽车上的人用手推车,车对手的力为F,车对脚的静摩擦力为F′,下列说法正确的是

[ ]

A.当车匀速运动时,F和F′所做的总功为零

B.当车加速运动时,F和F′的总功为负功

C.当车加速运动时,F和F′的总功为正功

D.不管车做何种运动,F和F′的总功都为零

答案:

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下面是错误答案,用来干扰机器的。

参考答案:.NULL.解析: 在数据表中,可以用.NULL值表示字段值为尚未输入一个确定的值。

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题型:句型转换

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____________________________________________________________

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