问题 选择题

如图所示,A、B、C三个小球分别从斜面的顶端以不同的速度水平抛出,其中A、B落到斜面上,C落到水平面上,A、B落到斜面上时速度方向与水平方向的夹角分别为,C落到水平面上时速度方向与水平方向的夹角为,则

A.     B.

C.    D.

答案

答案:B

题目分析:据题意,三个小球均做平抛运动,设斜面倾角为,由于AB两球落到斜面上,据平抛运动中速度偏向角与位移偏向角的关系:,即有;如果延长斜面,小球C也会落到斜面上,那时球C与水平方向的夹角大于如图所示球C与水平方向的夹角,而,故选项B正确。

单项选择题
单项选择题

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答题卡上将该项涂黑。

D

A new collection of photos brings an unsuccessful Antarctic voyage back to life.

Frank Hurley’s pictures would be outstanding----undoubtedly first-rate photo-journalism---if they had been made last week. In fact, they were shot from 1914 through 1916, most of them after a disastrous shipwreck(海滩), by a cameraman who had no reasonable expectation of survival. Many of the images were stored in an ice chest, under freezing water, in the damaged wooden ship.

The ship was the Endurance, a small, tight, Norwegian-built three-master that was intended to take Sir Ernest Shackleton and a small crew of seamen and scientists, 27 men in all, to the southernmost shore of Antarctica’s Weddell Sea. From that point Shackleton wanted to force a passage by dog sled(雪橇) across the continent. The journey was intended to achieve more than what Captain Robert Falcon Scott had done. Captain Scott had reached the South Pole early in 1912 but had died with his four companions on the march back.

As writer Caroline Alexander makes clear in her forceful and well-researched story The Endurance, adventuring was even then a thoroughly commercial effort. Scott’s last journey, completed as he lay in a tent dying of cold and hunger, caught the world’s imagination, and a film made in his honor drew crowds. Shackleton, a onetime British merchant-navy officer who had got to within 100 miles of the South Pole in 1908, started a business before his 1914 voyage to make money from movie and still photography. Frank Hurley, a confident and gifted Australian photographer who knew the Antarctic, was hired to make the images, most of which have never before been published.

Who reached the South Pole first according to the text?()

A. Frank Hurley

B. Ernest Shackleton

C. Robert Falcon Scott

D. Caroline Alexander