如图所示,在竖直平面内固定着半径为R的半圆形轨道,小球B静止在轨道的最低点,小球

题型:计算题

问题:

如图所示,在竖直平面内固定着半径为R的半圆形轨道,小球B静止在轨道的最低点,小球A从轨道右端正上方3.5R处由静止自由落下,沿圆弧切线进入轨道后,与小球B发生弹性碰撞。碰撞后B球上升的最高点C,圆心O与C的连线与竖直方向的夹角为60°。若两球均可视为质点,不计一切摩擦,求A、B两球的质量之比mA:mB

考点:动能定理
题型:计算题

The day of terror at the Virginia Polytechnic and State University in Blacksburg began at about 7:15 a. m. , with the shooting of a woman and a male resident adviser on the fourth floor of a dorm building on campus, Kristen Bensley, a freshman who lived below the floor where the shooting occurred, told TIME, "There were minors going on about the assailant was fighting with his girlfriend or something of that nature." Bensley notes that only residents can get into the building, using a specific "passport", that is, a card that one has to swipe in order to open doors before 10 a.m. If he was an outsider, someone would have had to let him in. Or more likely, he was a resident of the dorm himself. If so, how did be keep so much ammunition unnoticed

Unlike high schools, most universities can’t beef up security with a metal detector or two. So what can be done to protect students Other questions remain unanswered. Why was there a two-hour gap between the incident at the dorm and a far more fatal one across campus At one point, that led to theorizing that more than one gunman was involved. The gunman who killed at least 30 people at Norris Hall shortly after 9 a.m. was described by some sources as an Asian man.

It has been a surreal time for the students. Brandon Stiltner, a senior aerospace engineering student, and Jonathan Hess, a senior mechanical engineer, were watching TV all day but by noon they’d had enough. "We decided we needed to do something," Stiltner said. "We were worthless sitting around." So they took their six-foot Virginia Tech sign off the wall and logged into Facebook. Within the next few hours 100 people replied to their e-mail request for a vigil.

By 8 p.m. hundreds bf students began filing down the steps of the War Memorial Chapel toward the drill field. Clusters of two and three students stood together in silence. Slowly they began to line up to sign the board. "I’m still really in disbelief," says Stiltner. The shock of the day’s shootings sank in, Hess said, as he carried the sign across campus for the vigil. "It hit me," Hess said, "to know that it was in these buildings." The media crews that swarmed campus were also surreal to Hess and Stiltner. "We could look out our window and see exactly what’s on TV," Stiltner says. He watched his sign crowded with initials and prayers, awaiting the names of the victims, He shuddered. "I hope I don’t have any nasty surprises.

Which word can take place of "surreal" (Line 1, Para. 3; Line 5, Para. 4) in the passage()

A. Unbelievable

B.Unforgettable

C.Authentic

D. Miserable

题型:计算题

—Do you like the orange coat?

—Yes. I like it ________. [ ]

A. very much

B. a lot

C. at all

D. A or B

题型:计算题
当a为何值时,方程组
x-2y=-2a
2x+5y=a+6
的解x、y的值互为相反数.
题型:计算题

女,29岁,腹痛、腹泻5个月,粪便呈糊状,不含黏液与脓血,不伴有里急后重。体检:一般情况欠佳,消瘦,体温38℃,心肺无异常,最有价值的实验室检查为

A.血白细胞计数
B.血红蛋白测定
C.血沉
D.痰、粪便浓缩找结核杆菌
E.大便隐血试验

题型:计算题

就业是民生之本。增加贫困家庭劳动力就业,是治理贫困问题与环境问题的一把“金钥匙”。但增加就业有多种形式、多种途径。从治理贫困问题与环境问题的角度出发,根本的办法是增强市场化就业,而不是家庭内部的自雇就业,是增加异地就业,而不是当地就业。通过异地、市场化的就业,创造财富,转移人口,恢复生态,实现城乡协调发展,区域协调发展,经济社会协调发展,人与自然的和谐发展。根据上文推断以下不符合文意的一项是()。

A.农民进城打工

B.内地人口向沿海流动

C.到亲戚家帮佣

D.开办职业介绍所

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