问题 多选题

关于重力做功和物体的重力势能,下列说法中正确的是(  )

A.当重力对物体做正功时,物体的重力势能不一定减少

B.物体克服重力做功时,物体的重力势能一定增加

C.地球上任何一个物体的重力势能都有一个确定的值

D.重力做功的多少与参考平面的选取无关

答案

A、当重力对物体做正功时,说明物体下降,故重力势能减小,故A错误;

B、物体克服重力做功,说明重力做负功,物体上升,故重力势能增大,B正确;

C、重力势能的大小与零势能的选取有关,故地球上的物体其位置确定,但零势能面不确定的话,则其重力势能就不确定,故C错误;

C、重力做功与初末位置的高度差有关,与零势能的选取无关,故D正确;

故选:BD.

单项选择题
阅读理解

MAY 14 marks the 60th anniversary of the founding of the state of Israel(以色列). Many Israelis, however, are not in the mood to celebrate.

Looking at the damage to her neighbor's home from a Palestinian(巴勒斯坦) rocket, Batia Katar, a 17-year-old Israeli girl, was in tears. "We can't celebrate (Israel's) independence when things like this are happening," she said.

What is clear is that Israel is not a normal country. The country has a dramatic (戏剧性) history and ancient culture but has only officially existed for 60 years. Within hours after it was established in 1948, Israel was at war with its Arab neighbors for land. It won that time, and in 1956, 1967 and 1973, acquiring the West Bank, the Golan Heights, Gaza and east Jerusalem. For good or ill, Israelis can take pride in victories with so many countries. However, it occupied much more land than the United Nations agreed, which left local Palestinians homeless.

Different from all its neighbors in religion, Israel is also far more successful economically than its neighbors. Though, it gets a great amount of support from America and other Western countries. The country is now a world leader in many industries, such as IT and modern agriculture.

However, conflict exists, just like 60 years ago. And the signal of peace is as weak as ever. Palestinian militants (武装人员) have fired more than 7,000 missiles  from Gaza, mainly at Sedro, killing 13 people. In the same period hundreds of Palestinian civilians  in Gaza have died in Israeli military action.

In order to create peace, the world community hopes both sides accept and follow the Middle East peace plan. Optimists believe through Israeli-Palestinian negotiations there will finally be peace.

Both Israelis and Palestinians want to live in peace without explosions that remind them that they are living in a special but dangerous place.

小题1:  Why are many Israelis not in the mood to celebrate the both anniversary of the founding of the state of Israel? Because         .

A.the government didn't organize it

B.they are too busy to attend it

C.it is dangerous to celebrate it

D.conflicts and fights still exist小题2:  The underlined word established in the fourth paragraph means         .

A.defeated

B.founded

C.attacked

D.accepted小题3:  Israel is not a normal country because         .

A.the country has a dramatic history and ancient culture but has only officially existed for 60 years

B.within hours after its establishment, Israel was at war with its Arab neighbors for land

C.it occupied much more land than the UN agreed, which left local Palestinians homeless

D.all of the above小题4:  Which statement about Israel is NOT true according to the passage?

A.It became a country in 1948.

B.It is different from all its neighbors in religion.

C.It is now a world leader in many industries, such as IT and modern agriculture.

D.No country has supported it since it was founded.小题5:  It can be inferred from the passage that         .

A.it is still a question mark whether Israelis and Palestinians can live in peace

B.Israel was created as a homeland for homeless Jews

C.for good or ill, Israelis can take pride in victories with so many countries

D.Israel is far more successful economically than its neighbors