题目

如图所示，A、B两物块用一根轻绳跨过定滑轮相连(不计滑轮的质量和摩擦) ，静止于斜面体两个光滑斜面上的相同高度处，两斜面的倾角分别为α=60°和β=30°。现剪断轻绳，A、B 沿斜面下滑且斜面体保持静止，则从剪断轻绳到两物块着地的过程中（   ） A．地面对斜面体的静摩擦力为零 B．地面对斜面体有向右的静摩擦力 C．A、B两物块的重力势能的变化量相同 D．物块A的重力做功的平均功率大于物块B的重力做功的平均功率阅读理解The full moon climbs over the eastern horizon (地平线) and hangs like a huge orange globe in the sky. A few hours later, the moon is overhead but seems to have changed. The huge orange globe has become a small silver disk. What has happened? Why has the orange color disappeared? Why does the moon seem so much smaller and farther away now that it is overhead?The moon appears orange on the horizon because we view it through the dust of the atmosphere. The overhead moon does not really shrink as it moves away from the horizon. Our eyes inform us that the overhead moon is farther away. But in this position the moon is actually closer to our eyes than when it is near the horizon.The change in size is a trick our eyes and minds play on us. When the moon is low in the sky, we can compare its size with familiar objects. It is easy to see that the moon is much larger than trees or buildings, for example. When the moon is high in the sky, however, it is hard to compare it with objects on earth. Compared to the vastness of the sky, the moon seems small.There is another reason why the moon seems to shrink. We are used to staring at objects straight ahead of us. When an object is difficult to see, our eyes have to try to focus on it. When we move our heads back to look up, we will try hard again. Looking at something from an unaccustomed position can fool you into believing an object is smaller or farther away than it is. However, scientists do not yet understand completely why the moon seems to shrink as it rises in the sky.（1）What makes us puzzled when the moon is high in the sky?A.It becomes large.B.It looks different.C.Its color disappears.D.Its shape changes.（2）What really happens when the moon floats farther away from the horizon?A.It comes nearer.B.It turns orange.C.It goes farther.D.It gets through dust.（3）What does the author intend to suggest by mentioning trees and buildings in Para. 3?A.They can affect our judgment.B.They are low on earth.C.They can attract our attention.D.They are large objects.（4）What can we infer from the text?A.The size of the moon often changes.B.The moon is in fact a huge orange globe.C.The moon is beginning to shrink much.D.We do not see the moon as it really is.