问题 单项选择题

如图所示均质等截面杆OA位于铅垂面内,杆长L,重P,与水平夹角θ=60°。根据动静法计算AB绳突然剪断瞬时OA杆的角加速度为()。

A.(顺时针)

B.(逆时针)

C.(顺时针)

D.(逆时针)

答案

参考答案:C

解析:

本题为动静法的应用问题。

绳子剪断瞬时,OA杆绕O点转动,杆上惯性力包括:

由平衡方程∑MA=0,有:

解得(顺时针)。故选C。

单项选择题
单项选择题

Vienna was one of the music centers of Europe during the classical period, and Haydn, Mozart, and Beethoven were all active there. As the (1) of the Holy Roman Empire (which included parts of present-day Austria, Germany, Italy, Hungary, Czech and Slovakia), it was a (2) cultural and commercial center (3) a cosmopolitan character. Its population of almost 250,000 (in 1800) made Vienna the fourth largest city in Europe. All three (4) masters were born elsewhere, but they were (5) to Vienna to study and to seek (6) . In Vienna, Haydn and Mozart became close friends and influenced each other’s musical (7) . Beethoven traveled to Vienna at sixteen to play for Mozart; at twenty-two, he returned to study with Haydn.

Aristocrats from all over the Empire spent the winter in Vienna, sometimes bringing their private (8) . Music was an important part of court life, and a good orchestra was a (9) of prestige. Many of the nobility were excellent musicians.

Much music was heard in (10) concerts where aristocrats and wealthy commoners played (11) professional musicians. Mozart and Beethoven often earned money by performing in these intimate concerts. The nobility (12) hired servants who could (13) as musicians. An advertisement in the Vienna Gazette of 1789 (14) : " Wanted, for a house of the gentry, a manservant who knows how to play the violin well. "

In Vienna there was also (15) music, light and popular in (16) . Small street bands of wind and string players played at garden parties or under the windows of people (17) to throw (18) money. Haydn and Mozart wrote many outdoor entertainment (19) , (20) they called divertimentos or serenades. Vienna’s great love of music and its enthusiastic demand for new works made it the chosen city of Haydn, Mozart and Beethoven.

18()

A.off

B.away

C.about

D.down