题干

如图所示,带电平行金属板A、B,板间的电势差大小为U,A板带正电,B板中央有一小孔.一带正电的微粒,带电荷量为q,质量为m,自孔的正上方距板高h处自由落下,若微粒恰能落至A、B板的正中央C点,则(   )

A:微粒下落过程中重力做功为mg(h+ d2 ),电场力做功为 qU2

B:微粒落入电场中,电势能逐渐增大,其增加量为 qU2

C:若微粒从距B板高2h处自由下落,则恰好能达到A板

D:微粒在下落过程中动能逐渐增加,重力势能逐渐减小

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答案(点此获取答案解析)

B,C

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    More than anything else in the world, Lion liked being King of the jungle.  He walked around, showing off his power and pride.

    Each day Lion took a long lazy sleep under the shade of his favorite tree.  He always dreamed of weaker animals bowing(鞠躬) before him.

    One day Mouse ran through the jungle and tripped over Lion's huge paws.  Lion woke up with a start. “How dare you wake me up!” he shouted angrily. Lion grabbed(抓住) Mouse with one paw. “On the second thought, I'm in the mood for the snack, and you'll make a delicious meal.” he said.

    Mouse cried out, “King Lion, please spare(饶恕) me! If you let me live, I'll always remember your kindness.  And, some day, I might be able to help you.”

    “How could such a powerless little mouse ever help me?” That thought made Lion laugh so much that he decided to let Mouse go.  A week later, Lion was walking through the jungle on the way to his favorite tree when he stepped onto a hunter's net.  The net scooped him up. No matter how he twisted (扭动) and turned, he couldn't escape.

    When Mouse heard Lion's frightened shouts, he raced to help. Mouse quickly chewed(咬)through the ropes to make a hole in the net.  Soon, Lion moved out and was free. Lion looked down at the little mouse. “Thank you for saving my life,” said Lion, smiling his widest smile.  “I was mistaken.  You are not a powerless little mouse. You are a great friend!”