题干

质量相等的甲、乙两车从某地同时由静止开始沿直线同方向加速运动,甲车功率恒定,乙车牵引力恒定,两车所受阻力相等且均为恒力.经过t时间,甲、乙两车速度相同,则(    )

A:t时刻甲车一定在乙车的前面

B:t时刻甲车加速度大于乙车加速度

C:t时刻甲车牵引力的瞬时功率大于乙车牵引力的瞬时功率

D:t时间内甲车牵引力的平均功率小于乙车牵引力的平均功率

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A

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Some years ago, writing in my diary used to be a usual activity.I would return from school and spend the expected half hour recording the day'sevents, feelings, and impressions in my little blue diary. I did not reallyneed to express my emotions by way of words, but I gained a certainsatisfaction from seeing my experiences forever recorded on paper. After all,isn't accumulating memories a way of preserving the past?

When I was thirteen years old, I went on a long journey on footin a great valley, well equipped with pens, a diary, and a camera. During thetrip, I was busy recording every incident, name and place I came across. I feltproud to be spending my time productively, dutifully preserving for futuregenerations a detailed description of my travels. On my last night there, Iwandered out of my tent, diary in hand. The sky was clear and lit by the glareof the moon, and the walls of the valley looked threatening behind their screenof shadows. I automatically took out my pen...

At that point, I understood that nothing I wrote could evermatch or replace the few seconds I allowed myself to experience the dramaticbeauty of the valley. All I remembered of the previous few days were the dullcharacterizations I had set down in my diary.

Now, I only write in my diary when I need to write down aspecial thought or feeling. I still love to record ideas and quotations thatstrike me in books, or observations that are particularly meaningful. I takepictures, but not very often only of objects I find really beautiful. I'm nolonger blindly satisfied with having something to remember when I grow old. Irealize that life will simply pass me by if I stay behind the camera, busypreserving the present so as to live it in the future.

I don't want to wake up one day and have nothing but a pile ofpictures and notes. Maybe I won't have as many exact representations of peopleand places; maybe I'll forget certain facts, but at least the experiences willalways remain inside me. I don't live to make memories--I just live, and thememories form themselves.