题干

掉在水平地面上的弹性小球会被弹起,而且弹跳的高度会越来越低.图所示是小球弹跳的频闪照片,MN为等高线,小球在3、5位置的高度一样.不计空气阻力,则:(1)小球在图中位置____时的势能最大;(2)小球在位置3和位置5时比较,它们的机械能____(填“相等”或“不相等”)(3)小球从位置____到位置4的过程中,动能转化为势能.

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答案(点此获取答案解析)

1,不相等,3

同类题3

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    In 1978, I was 18 and was working as a nurse in a small town about 270 km away from Sydney, Australia. I was looking forward to having five days off from duty. Unfortunately, the only one train a day back to my home in Sydney had already left. So I thought I'd hitch a ride (搭便车).

    I waited by the side of the highway for three hours but no one stopped for me. Finally, a man walked over and introduced himself as Gordon. He said that although he couldn't give me a lift, I should come back to his house for lunch. He noticed me standing for hours in the November heat and thought I must be hungry. I was doubtful as a young girl but he assured (使……放心) me I was safe, and he also offered to help me find a lift home afterwards. When we arrived at his house, he made us sandwiches. After lunch, he helped me find a lift home.

Twenty-five years later, in 2003, while I was driving to a nearby town one day, I saw an elderly man standing in the glaring heat, trying to hitch a ride. I thought it was another chance to repay someone for the favor I'd been given decades earlier. I pulled over and picked him up. I made him comfortable on the back seat and offered him some water.

    After a few moments of small talk, the man said to me, “You haven't changed a bit, even your red hair is still the same.”

    I couldn't remember where I'd met him. He then told me he was the man who had given me lunch and helped me find a lift all those years ago. It was Gordon.