一个重为400N的木箱放在水平地面上,要是他从原地移动,最少要用100N的水平推

题型:选择题

问题:

一个重为400N的木箱放在水平地面上,要是他从原地移动,最少要用100N的水平推力。当木箱被推动之后,只要用90N的水平推力就可以使木箱沿水平地面作匀速直线运动。对于以上所述的过程中

A.木箱与地面间的最大静摩擦力大小为90N

B.木箱与地面间的滑动摩擦力大小为90N

C.木箱与地面间摩擦力大小始终为100N

D.当用120N的水平推力推木箱时,木箱与地面间的摩擦力为120N

考点:静摩擦力滑动摩擦力、动摩擦因数
题型:选择题

属于脑膜刺激征的是()

A.Kerning征

B.Babinski征

C.Gordon征

D.Brudzinski征

E.颈强直

题型:选择题

房产税的征税范围不包括( )。

A.城市

B.农村

C.县城

D.建制镇

题型:选择题

It seems parents have long been right. Going to bed early is key to getting enough sleep and helping adolescents feel on top of the world, a new study reported.

A   1  of sleep among youngsters may    2  depression and suicidal (自杀的)thoughts, according to the study by the Columbia University Medical Center.

"Our results are   3  with the theory that inadequate sleep is a risk factor for depression, working with other   4  and protective factors through multiple possible causal pathways to the development of this   5  disorder," said lead author James Gangwisch.

"  6  quality sleep could therefore be a preventative measure against   7  and a treatment for depression," he added in the study   8  in the Friday issue of Sleep magazine.

The study followed the nightly habits of some 15,659 college and high-school students, and   9  those who consistently went to bed   10  midnight had a 24 percent higher risk of depression than those who turned in before 10:00 pm.

Night owls(夜猫子)also ran a 20 percent   11  risk of battling suicidal thoughts, the study added.

The American Academy of Sleep Medicine   12  that adolescents should sleep at least nine hours or more a night. Those who were tucked in before 10:00 pm reported they slept    13  about eight hours and 10 minutes.

But that amount of sleep  14  significantly for those in bed after midnight.

And adolescents who slept five hours or less a night were 71 percent more   15  to suffer depression and 48 percent more     16  becoming suicidal, the study said.

"It is a common perception and societal   17  that adolescents do not need as much sleep as pre-adolescents, yet studies suggest that adolescents may  18  require more sleep," said Gangwisch.

"Studies have found that adolescents do not go to bed   19  enough to make up for earlier school start times, and transitions to earlier school start times have been shown to be   20  with significant sleep deprivation(剥夺). "

(    ) 1. A. night                B. moderation       C. limit                D. lack

(    ) 2. A. result in           B. lie in                C. come about       D. bring in

(    ) 3. A. opposed           B. mixed              C. related              D. consistent

(    ) 4. A. risk                  B. chance              C. potential           D. reason

(    ) 5. A. mood                      B. body                C. feeling             D. mind

(    ) 6. A. little                B. lack                 C. Adequate          D. over

(    ) 7. A. suffering          B. depression               C. disorder            D. sadness

(    ) 8. A. reported           B. published          C. reflected           D. noted

(    ) 9. A. found                      B. investigated      C. appraised          D. supported

(    ) 10. A. before            B. from                C. by                    D. after

(    ) 11. A. lower             B. higher              C. more                D. less

(    ) 12. A. appeals           B. recommends     C. calls                 D. plans

(    ) 13. A. on average      B. in place            C. ahead of           D. in number

(    ) 14. A. increased               B. disappeared       C. strengthened     D. dropped

(    ) 15. A. likely             B. probable           C. possible            D. perhaps

(    ) 16. A. at sight of       B. at risk of          C. in front of               D. as a result of

(    ) 17. A. wish               B. expectation       C. suggestion               D. attempt

(   ) 18. A. exactly           B. immediately      C. directly            D. actually

(    ) 19. A. early              B. lately                      C. soon                 D. quickly

(    ) 20. A. separated               B. associated         C. divided             D. depended

题型:选择题

如图所示,一物体以初速度v0冲向光滑斜面AB,并恰好能沿斜面升高h,下列说法中正确的是

[ ]

A.若把斜面从C点锯断,物体冲过C点后仍升高h

B.若把斜面弯成圆弧形D,物体仍沿圆弧升高h

C.若把斜面从C点锯断或弯成圆弧状,物体都不能升高h

D.若把斜面AB变成曲面AEB,物体沿此曲面上升仍能到B点

题型:选择题

以下关于集中锅炉房布置原则的表述,正确的是( )。

A.远离热负荷比较集中的地区
B.便于引出管道,并使室外管道的布置在技术、经济上合理
C.季节性运行的锅炉房宜位于该季节盛行风向的上风向
D.全年运行的锅炉房宜位于居住区和主要环境保护区的全年最小频率风向的下风向

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