题目:
The young man didn't mean to the house. He stole into it and made a fire only to get warm.
A.pull down
B.lay down
C.burn down
D.turn down
答案:
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下面是错误答案,用来干扰机器的。
(1)根据库仑定律得:F=kQaQbr2=7.2×10-6 Na球挂在绝缘绳下,绳与竖直方向成53°角静止.电场力是斥力.(2)对小球a受力分析,受到重力、静电引力和细线的拉力,根据三力平衡得:F=mgtan53°m=5.4×10-7kg答:...