如图所示，A、B两质点从同一点O分别以相同的水平速度v0沿x轴正方_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题多选题

如图所示，A、B两质点从同一点O分别以相同的水平速度v₀沿x轴正方向抛出，A在竖直平面内运动，落地点为P₁；B沿光滑斜面运动，落地点为P₂，P₁和P₂在同一水平面上，不计阻力，则下列说法正确的是（　　）

A．A、B的运动时间相同

B．A、B沿x轴方向的位移大小相同

C．A、B运动过程中的加速度大小不相同

D．A、B落地时的速度大小相同

答案

A、A质点做平抛运动，根据平抛规律得

A运动时间t=

2h

g

，

B质点视为在光滑斜面上的类平抛运动，其加速度为gsinθ，

B运动时间t′=

2h

gsinθ2

，故A错误．

B、A、B沿x轴方向都做水平速度相等的匀速直线运动，由于运动时间不等，所以沿x轴方向的位移大小不同，故B错误．

C、A、B运动过程中的加速度大小分别是g和gsinθ，故C正确．

D、根据动能定理得A、B运动过程中：：

mgh=

1

2

mv2-

1

2

mv

20

v=

2gh

+v

20

，故D正确．

故选CD．

单项选择题

When Liam McGee departed as president of Bank of America in August, his explanation was surprisingly straight up. Rather than cloaking his exit in the usual vague excuses, he came right out and said he was leaving “to pursue my goal of running a company.” Broadcasting his ambition was “very much my decision,” McGee says. Within two weeks, he was talking for the first time with the board of Hartford Financial Services Group, which named him CEO and chairman on September 29.
McGee says leaving without a position lined up gave him time to reflect on what kind of company he wanted to run. It also sent a clear message to the outside world about his aspirations. And McGee isn’t alone. In recent weeks the No.2 executives at Avon and American Express quit with the explanation that they were looking for a CEO post. As boards scrutinize succession plans in response to shareholder pressure, executives who don’t get the nod also may wish to move on. A turbulent business environment also has senior managers cautious of letting vague pronouncements cloud their reputations.
As the first signs of recovery begin to take hold, deputy chiefs may be more willing to make the jump without a net. In the third quarter, CEO turnover was down 23% from a year ago as nervous boards stuck with the leaders they had, according to Liberum Research. As the economy picks up, opportunities will abound for aspiring leaders.
The decision to quit a senior position to look for a better one is unconventional. For years executives and headhunters have adhered to the rule that the most attractive CEO candidates are the ones who must be poached. Says Korn/Ferry senior partner Dennis Carey:” I can’t think of a single search I’ve done where a board has not instructed me to look at sitting CEOs first.”
Those who jumped without a job haven’t always landed in top positions quickly. Ellen Marram quit as chief of Tropicana a decade age, saying she wanted to be a CEO. It was a year before she became head of a tiny Internet-based commodities exchange. Robert Willumstad left Citigroup in 2005 with ambitions to be a CEO. He finally took that post at a major financial institution three years later.
Many recruiters say the old disgrace is fading for top performers. The financial crisis has made it more acceptable to be between jobs or to leave a bad one. “The traditional rule was it’s safer to stay where you are, but that’s been fundamentally inverted,” says one headhunter. “The people who’ve been hurt the worst are those who’ve stayed too long.”

The word “poached” (Line 3, Paragraph 4) most probably means

A．approved of.
B．attended to.
C．hunted for.
D．guarded against.

判断题

要删除整个表格．先选中表格中的所有行，然后按Del键即可。( )