题目内容

一水平圆盘可绕通过其中心的固定竖直轴转动,盘上站着一个人.把人和圆盘取作系统,当此人在盘上随意走动时,若忽略轴的摩擦,此系统

A. 动量守恒
B. 机械能守恒
C. 对转轴的角动量守恒
D. 动量、机械能和角动量都守恒
E. 动量、机械能和角动量都不守恒

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将细绳绕在一个具有水平光滑轴的飞轮边缘上,现在在绳端挂一质量为m的重物,飞轮的角加速度为a.如果以拉力2mg代替重物拉绳时,飞轮的角加速度将

A. 小于a
B. 大于a,小于2 a
C. 大于2a
D. 等于2a

Honour means:a. to pay at sight if the credit is available by sight payment.b. to incur a deferred payment undertaking and pay at maturity if the credit is available by deferred payment.c. to accept a bill of exchange (“draft”) drawn by the beneficiary and pay at maturity if the credit is available by acceptance.

原产地证明书的种类有哪些？

一般原产地证书的作用是什么？应该向哪个部门申领？