题干

一物体从静止开始由倾角很小的光滑斜面顶端滑下,保持斜面底边长度不变,逐渐增加斜面长度以增加斜面倾角.在倾角增加的过程中(每次下滑过程中倾角不变),物体的加速度a和物体由顶端下滑到底端的时间t的变化情况是(  )

A:a增大,t增大

B:a增大,t变小

C:a增大,t先增大后变小

D:a增大,t先变小后增大

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答案(点此获取答案解析)

D

同类题5

通读下面的短文,掌握其大意,然后从各题所给的A、B、C三个选项中选出一个最佳答案。

    “Everything happens for the best.”Whenever I faced 1my mother would say so.

    After I2 from college in 1932, I decided to find a job in radio as a sports announcer (广播员). I went to Chicago and knocked at the door of every station. But 3 I was refused every time.

    At one station, a kind lady told me that big stations wouldn't want an inexperienced person and suggested that I try my luck at smaller stations. Following her 4 I went back to Dixon, where I had grown up. There were no radio-announcing jobs in Dixon, and my father said a newly-opened store wanted a local athlete to work for it. I asked for the job, but I was 5again.

    “Everything happens for the best,”Mom 6 me. Dad offered me the car to look for a job. I tried WOC Radio in Davenport, Iowa. The program director, Peter MacArthur, said they had hired an announcer.

    As I left his office, my frustration (挫败感) boiled over.“How can I become a sports announcer 7 I can't get a job in a radio station?”I asked aloud.

    While I was waiting for the lift, I heard someone 8my name. It was MacArthur.“What was that you said about sports? Do you know anything about football?”Then he asked me to broadcast (广播) an imaginary game.9 with my performance, he offered me a chance to work there.

    10my way home, I thought of my mother's words:“If you carry on, one day something good will happen. Something wouldn't have happened if not for that previous (之前的) disappointment.”