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[主观题]
如图,轻质光滑长木板AB可绕O转动,A端用竖直绳与地板上拉着,在离O点0.4m的B处拄一密度为0.8×103kg/m3;长20cm的长方形物体,当物体浸入水中10cm深处静止时,从盛满水的溢水口的杯中溢出0.5N的水(g=10N/kg)()
A.物体受到的浮力0.5NB.木板B端所受拉力0.3NC.当一质量为200g的球从O点以2cm/s的速度沿木板向A端匀速运动时 ,系在A端的绳拉力刚好为零,则球由O点出发多少时间 为3sD.物体的重力1N
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ABC
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