问题 问答题

滚摆下落,越滚越快,是将______能转化为______能.卫星从近地点飞行到远地点将______能转化为______能.

答案

(1)滚摆在高出时,其质量不变,其高度大,速度小,故其重力势能大,其动能小;当其在加速下落时,其质量不变,但速度变快,故其动能变大,同时其高度减小,故其重力势能变小,所以该过程是将重力势能转化为动能的过程;

(2)在远地点,卫星距地面的高度最高,重力势能最大,飞行最慢,动能最小.在近地点,卫星距地面的高度最低,重力势能最小,飞行最快,动能最大.故卫星从近地点飞行到远地点将动能转化为重力势能的过程.

故答案为:重力势;动;动;重力势.

单项选择题

I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.

It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .

They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.

The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop"

Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) She had only one small, flat bag with a few candies—fiftycent candies I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.

"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "

I never felt so (20) as I did that day.

18()。

A.since 

B.after 

C.while 

D.until

多项选择题