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问题 选择题

某人在静止的湖面上竖直上抛出一个铁球，铁球升到最高点后自由下落，穿过湖水并陷入湖底的淤泥中一段深度，铁球所受阻力随时间变化的图像如图甲所示，以v、a、F、Ek分别表示小球的速度、加速度、所受合外力和动能四个物理量。乙图中能正确反映运动过程各量随时间变化的是

答案

AC

分析：速度图象中速度大于0表示物体沿正方向运动，速度小于0表示物体沿负方向运动；速度图象的斜率等于物体的加速度；斜率的绝对值越大代表物体的加速度越大．

解答：解：物体在竖直上升过程中物体的速度竖直向上，即速度大于0，此时物体的加速度为a1=g，方向竖直向下；合外力为重力

到达最高点后做自由落体运动，速度方向竖直向下，即速度小于0，此时物体的加速度加速度为a2=g，方向竖直向下，合外力为重力

故进入湖水之前物体的加速度保持不变．故速度图象的斜率保持不变．

铁球进入湖水后受到湖水的阻力作用，但重力大于阻力，加速度向下但加速度a3＜g，合外力小于重力，但方向向下，速度方向仍然向下即速度小于0．

在淤泥中运动的时候速度仍向下，即速度小于0，但淤泥对球的阻力大于铁球的重力，合外力向上，所以加速度方向竖直向上，故物体做减速运动．

故AC正确．

故选AC．

点评：把握物体的运动情况包括速度方向和加速度的大小和方向是解决此题的关键，所以解决运动学问题要详细进行过程分析和受力分析．

阅读理解
阅读下列短文，根据所读内容在表格中的空白处填入恰当的单词。
注意：表格中每个空格只填一个单词。
     Having entered a hoarding school, Ada and her twin sister Rita determined to strike out independently.
Although the sisters had requested rooms in different dorms, they were placed in the same, Ada on the eighth
floor and Rita one floor higher. While Ada lived in harmony with her roommate, Rita was unhappy. She and
her roommate had a quarrel over matters like the smallest thing-the time of lights being turned off-and the
biggest thing-the arrangement of the furniture. Finally, they communicated primarily through short notes rather
than by speaking. Rita kept running down along the stairs to ask Ada for help. Before long, the two wanted to
live together again. Rita's roommate finally had to move out.
     Rita's ability to solve her problem by rooming with her twin is unusual, but the conflict she faced is not.
Despite great efforts by many schools to make good roommate matches, unpleasant outcomes are common.
     Most conflicts between roommates develop from small, annoying differences. In extreme cases, the
conflicts can lead to serious violence and affect roommates' psychological (心理的) health.
     Learning to tolerate a stranger's habits may teach students the art of compromise, hut the learning process
is often painful.
     Many schools have started conflict solution programs to calm tensions that could build up like a volcano
preparing to explode, resulting in physical violence. Some schools try to prevent conflicts by using
computerized matching. Students are put together on the basis of their answers to housing form questions
about preferred hours of study and sleep, and self-described tendencies toward tidiness or disorder. Parents
sometimes weaken the process by taking the forms and filling in false data about their children's habits.
     If only conflicts between roommates could disappear!
TitleRoommate (1)_______
Example Rita, living on the (2)_______ floor, quarreled with her roommate over
matters (3)_______ from when lights should be turned off to how the
furniture should be arranged before they gave up on oral communication.
Rita kept running (4)_______ to seek comfort from her twin sister. They
finally (5)_______ the room again.
(6)_______            Though many schools try to make (7)_______ roommates, conflicts
between roommates still exist.
Bad results● Leading to serious physical violence. 
● (8)_______ roommates' psychological health.
Solutions ● Learning the art of (9)_______. 
● Tolerating a stranger's habits. 
● Using computerized matching.
WishConflicts between roommates could be (10)_______.
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单项选择题

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