问题 多选题

如图所示,一个内壁光滑的圆锥形筒的轴线垂直于水平面,圆锥筒固定不动,两个质量相同的小球A和B紧贴着内壁分别在图中所示的水平面内做匀速圆周运动,则(  )

A.球A的线速度一定大于球B的线速度

B.球A的角速度一定小于球B的角速度

C.球A的运动周期一定小于球B的运动周期

D.球A对筒壁的压力一定大于球B对筒壁的压力

答案

A、对小球受力分析,受重力和支持力,如图

根据牛顿第二定律,有

F=mgtanθ=m

v2
r

解得

v=

grtanθ

由于A球的转动半径较大,故线速度较大,故A正确;

B、ω=

v
r
=
gtanθ
r
,由于A球的转动半径较大,故角速度较小,故B正确;

C、T=

ω
=2π
r
gtanθ
,由于A球的转动半径较大,故周期较大,故C错误;

D、由A选项的分析可知,压力等于

mg
cosθ
,与转动半径无关,故D错误;

故选AB.

完形填空

After Mom died, I began visiting Dad every morning before I went to work. He was weak. He always put a glass of  1     on the kitchen table for me, with a note reading, “Drink your juice.”

As a kid, I once    2   Mom, “Why doesn’t Dad love me?”Mom asked me, “   3  ? Why do you think so?”“Well, he never tells me,” I said.“But    4  , how hard he works to take care of us. That’s how he    5   his love.”

Many years later, after drinking the juice, I hugged(拥抱) my father and said, “I love you, Dad.” From then on, I did that every   6  . My father never told me how he felt about my hugs.

Then one day, I didn’t hug him and just   7   towards the door. Dad said, “Well?”

“Well, what?” I asked. “Well…” he said again, holding out his    . Then I hugged him, and told him, “I’m fifty years old, Dad. You’ve   9   told me you love me.” A minute later, Dad said, “All right! I    10   you.” Although he spoke in a very low voice, I heard it clearly.

小题1: A. water              B. juice                C. wine

小题2: A. asked              B. surprised            C. told

小题3: A. When               B. What                 C. How

小题4: A. watch              B. look                 C. see

小题5: A. kisses             B. does                 C. shows

小题6: A. morning            B. afternoon            C. evening

小题7: A. arrived            B. came                 C. moved

小题8: A. arms               B. head                 C. neck

小题9: A. always             B. never                C. usually

小题10: A. hate              B. miss                 C. love

单项选择题