题干

如图所示,在倾角为θ的光滑斜面上,存在着两个匀强磁场,磁场Ⅰ垂直斜面向上、磁感应强度大小为B,磁场Ⅱ垂直斜面向下、磁感应强度大小为3B,磁场的宽度MJ和JG均为L,一个质量为m、电阻为R、边长也为L的正方形导线框,由静止开始沿斜面下滑,当ab边刚越过GH进入磁场Ⅰ区时,线框恰好以速度v1做匀速直线运动;当ab边下滑到JP与MN的中间位置时,线框又恰好以速度v2做匀速直线运动,从ab进入磁场Ⅰ至ab运动到JP与MN中间位置的过程中,线框的机械能减少量为ΔE,重力对线框做功的绝对值为W1,安培力对线框做功的绝对值为W2,下列说法中正确的是(  )

A:v1∶v2=4∶1

B:v1∶v2=9∶1

C:ΔE=W1

D:ΔE=W2

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答案(点此获取答案解析)

B,D

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阅读理解

    Many years ago three soldiers, hungry and tired of battle, came upon a small village. The villagers, suffering a bad harvest and the many years of war, quickly hid what little they had to eat and met the three in the village square, shaking their heads and sighing, “Well, we are starving.” The soldiers communicated with each other quietly and then the first soldier turned to the villagers. “Your poor fields have left you nothing to share, so we will share what little we have: the secret of making soup from stones.”

    Naturally the villagers were intrigued and soon a fire was built to the villager's greatest pot, and then the soldiers dropped in three smooth stones.

     “Now this will be a fine soup,” said the second soldier, “but a handful of salt and some parsley (香芹) would make it wonderful!” Up jumped a villager, crying “What a piece of luck! I've just remembered where some has been left!”

    And off she ran, returning with parsley. As the pot was boiling, the memory of the villagers improved: soon carrots, beef and cream had found their way into the great pot. They ate and danced and sang well into the night, thrilled about the feast and their new-found friends. In the morning the three soldiers awoke, finding all the villagers standing before them. At their feet lay a bag of the village's best bread and cheese. “You have given us the greatest gift.” said an elder, “and we shall never forget.” The third soldier turned to the crowd, and said, “There is no secret, but this is certain: people working together can accomplish great things.” At last the light dawned on villagers. Off the soldiers wandered, down the road.