题干

公路上匀速行驶的货车受一扰动,车上货物随车厢底板上下振动但不脱离底板.一段时间内货物在竖直方向的振动可视为简谐运动,周期为T.取竖直向上为正方向,以某时刻作为计时起点,即t=0,其振动图象如图所示,则              (  )

A:t=T时,货物对车厢底板的压力最大

B:t=T时,货物对车厢底板的压力最小

C:t=T时,货物对车厢底板的压力最大

D:t=T时,货物对车厢底板的压力最小

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答案(点此获取答案解析)

C

同类题2

    One day, I went to see my last patient(病人), an old woman. In the doorway, I saw she was struggling (挣扎) to put socks on her swollen (浮肿)feet in the bed. I stepped in, spoke quickly to the nurse, read her chart noting. I was almost in the clear that she was not in serious condition.
I asked, “Could I help put on your socks? How are you feeling? Your sugars and blood pressure were high but they’re better today. The nurse mentioned you’re anxious to see your son. He’s visiting you today. It’s nice to have a family visit. I think you really look forward to seeing him."
    "Sit down, doctor. This is my story, not yours." She said with a serious voice.
I was surprised as I helped her with the socks. She told me that her only son lived around the corner from her, but she had not seen him in five years. She believed that was the main cause of her health problems. After hearing her story and putting on her socks, I asked if there was anything else I could do for her. She shook her head no and smiled. All she wanted me to do was to listen.
    Each story is different. Some are detailed; others are simple. Some have a beginning, middle and end; others don’t have clear ends. Some are true; others not. Yet all those things do not really matter. What matters to the storyteller is that the story is heard — without interruption(打断) or judgment(评价).
    It was that woman who taught me the importance of stopping, sitting down and truly listening. And, not long after, in an unexpected accident, I became a patient. 20 years later, I sit all the time — in a wheelchair.
For as long as I could, I continued to see patients from my chair. I believe in the power of listening.