英语周报2019年2022，英语29期的答案

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【解析】(1)设小球的质盘为m初速度为v,从O点到A点小球水平方向做匀速直线运动,有2L=vlo①(1分)从A点运动到B点小球水平方向做匀减速直线运动,由题意知,小球在B点水平方向的分速度为0由运动学公式得L=u②②联立解得m-0即一士(2)设小球在B点竖直方向上的速度为,有4E=m③(1分)又EM0=2(1分)设小球在A点竖直方向上的速度为vo,由于小球在竖直方向做自由落体运动,且to=tA因此w=B⑤分1③④⑤联立解得(1分)从A点运动到B点,小球水平方向做匀减速直线运动,由牛顿第二定律和运动学公式得=2EL⑦分④⑦联立解得E=B,方向水平向左(1分)又由运动学公式得w=glos⑧(1分)BELne(1分)E⑥③③联立解得m=3gL(1分)

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