如图所示，质量为m的小球A沿高度为h倾角为θ的光滑斜面以初速v0_爱下问搜题

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问题选择题

如图所示，质量为m的小球A沿高度为h倾角为θ的光滑斜面以初速v₀滑下，另一质量与A相同的小球B自相同高度同时由静止落下，结果两球同时落地．下列说法正确的是（　　）

A．重力对两球做的功不等

B．落地前的瞬间A球的速度等于B球的速度

C．落地前的瞬间A球重力的瞬时功率大于B球重力的瞬时功率

D．两球重力的平均功率相同

答案

A、根据W=mgh知，重力对两球做功相同．故A错误．

B、对A球，根据动能定理得，mgh=

1

2

mv_A²-

1

2

mv₀²，对B球，根据动能定理得，mgh=

1

2

mv_B²，知v_A＞v_B．故B错误．

C、两球都做匀变速直线运动，运动时间相等，v_A=gsinθt，v_B=gt，A球重力做功的瞬时功率P=mgv_Asinθ=mg²sin²θt，B球重力做功的瞬时功率P′=mgvB=mg2t．知A球的重力瞬时功率小于B球重力的瞬时功率．故C错误．

D、两球重力做功相等，时间相等，根据P=

W

t

知，重力的平均功率相等．故D正确．

故选D．

完形填空

This might seem crazy, because many students in the United States do job     being paid! Yes, they volunteer. And they     it, too! Many girls volunteer to work in hospitals. Other kids volunteer to work at zoos or dog houses where lost       are kept in._     they don't get paid, they get to      _ their days with animals. There's also a Big Brother Foundation in the US. Older kids can _     younger kids and them with their homework.
Maybe you don't have _    chances in China to volunteer as kids in the US have. So be creative and try to _     _ some ideas! Volunteer to help people in _     _ way you can think of. You can volunteer to help at a hospital, you can help old people, or you can volunteer to clean up trash on the ground.
_     _ volunteer? Because it can give you a good _     _.It might help you get a job in the future. Doing volunteer work shows that you care about other__     _ and you are generous with your time. Bosses like people _     _ do these things. Volunteering not only helps you in the future, but also makes you feel _     _ now. Try it! It could be the best improvement to _     _ vacations.

A．even though

C．come up with

C．more worried

单项选择题

女患，65岁，以"突然不能说话，左侧肢体无力，约5～6分钟恢复，反复发作3天"为主要表现来诊。查体：神清语利，脑神经检查未见明显异常，四肢活动自如，双侧Babinski征（-）。首先应考虑的诊断是（）

A.局灶性癫痫发作

B.脑栓塞

C.癔症发作

D.颈内动脉系统短暂性脑缺血发作

E.椎-基底动脉系统短暂性脑缺血发作