(上课用)共点力的平衡.ppt

牛顿运动定律的应用(二) 牛顿运动定律的应用(二) (共点力的平衡) (共点力的平衡) Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 例题: ? 一个人站在体重计的测盘上,在人下蹲的过程中,指针示数变化应是( ) ,后还原 ,后还原 ,后增加,再还原复复习习旧旧知知 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 解析:人下蹲的过程经历了加速向下、减速向下和静止这三个过程. ,人获得向下的加速度 a,由牛顿第二定律得: mg agmF ma F mg N N?????)(由此可知,弹力 F N将小于重力 mg . 复复习习旧旧知知 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. ,人获得向上的加速度 a,由牛顿第二定律得: mg agmF ma mg F N N?????)(由此可知,弹力 F N将大于重力 mg . F N= mg . 所以,正确选项为 D. 复复习习旧旧知知 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose