八年级英语周报新目标2021到2020答案

14.解：(1)物体B从释放到细绳刚绷直做自由落体运动，设细绳绷直前物体B的速度大小为v,绷直后A、B的共同速度大小为v共，A、B共同向下减速时的加速度大小为a,有2=2gh(2分)mBU=(mA十mB)哄(2分)哄2=2aH(2分)mA8一mBg=(mA十mB)a(2分)解得h=1.25m。(1分)(2)由(1)知当物体A第一次落地时，物体B的速度大小为~共=2/s,方向向上，此后物体B做竖直上抛运动，有h'=H U2g(2分)解得h'=1.2m。(2分)3/m

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