题干

关于重力,下列说法中正确的是(   )

A:向上抛出去的排球,在上升过程中不受重力的作用

B:汽车在斜坡上行驶,受到的重力垂直于坡面

C:物体的重心总是在物体上

D:地球附近的物体在没有支撑的时候,要落向地面,是因为受到重力的作用

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答案(点此获取答案解析)

D

同类题4

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    We were on a visit to Monkey Island. Jim thought we should try water skiing(滑水).

    We can get a boat and ski at Monkey Island.

   Don't go water skiing near Monkey Island today,” said the woman standing near the boats. “There might be sharks(鲨鱼) in the water.”

    “I don't think so.” said Jim who thought he knew everything.

    “I wouldn't go water skiing in the sea near Monkey Island today,” said the man with the woman. “They saw sharks in the water yesterday.”

    “The sharks won't hurt me,” said Jim with a big smile on his face.

      Another man getting out of a boat said, “I'm sure we just saw a shark in the water a few minutes ago.”

    “Don't worry about me,” said Jim. “I don't worry about sharks.”

    Jim and his two friends, Bill and Bruce pushed the boat into the water. Jim was driving the boat. He drove very fast and sprayed water on everyone standing near the boat.

    Jim drove the boat to the middle of the sea near Monkey Island. Everyone could see him and the boat. He wanted to show everyone how well he could water ski.

    “You drive the boat, Bill,” Jim said. “Bruce, you watch me and the rope while I water ski.”

    “What about the sharks?” asked Bill.

    “Forget about the sharks,” said Jim. “I'm not afraid of sharks.”

    Jim got into the water. He was putting his feet in the water skis. Then Jim felt something large and hard touch his leg as it swam past him. Suddenly, a brown fin(鳍) moved through the water towards Jim.

    Later, when Bill and Bruce stopped laughing, they said, “We never saw anyone move so fast! You were running on top of the water to get back in the boat! You even left the water skis in the water.

    “There it is again! Shark! Shark!” cried Jim.

    Everyone laughed----even the people standing on shore.

    The dolphin(海豚) came to surface again, took a deep breath, smiled at Jim and went back down into the deep water.