物体做下列几种运动，其中遵守机械能守恒的是 ( )
A．自由落体运动
B．在竖直方向做匀速直线运动
C．在水平面内做匀变速直线运动
D．在竖直平面内做匀速圆周运动
答案：A
考点：
分析：物体机械能守恒的条件是只有重力或者是弹力做功，根据机械能守恒的条件逐个分析物体的受力的情况，即可判断物体是否是机械能守恒．
解答：解：A、做自由落体运动的物体只受重力的作用，所以机械能守恒，所以A的说法正确．
B、物体在竖直方向做匀速直线运动，说明物体受力平衡，除了重力之外还有其他的外力的作用，并且其他的外力对物体做功，所以机械能不守恒，所以B错误．
C、在水平面内做匀变速直线运动，重力势能不变，动能增加，所以机械能增加不守恒，所以C的说法错误．
D、在竖直平面内做匀速圆周运动，动能不变，重力势能变化，所以机械能不守恒，所以D的说法错误．
故选A．
点评：本题是对机械能守恒条件的直接考查，掌握住机械能守恒的条件即可，题目比较简单．
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