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问题 选择题

一物体静止在升降机的地板上，在升降机加速上升的过程中，地板对物体的支持力所做的功等于（  ）

A．物体势能的增加量

B．物体动能的增加量加上物体势能的增加量

C．物体动能的增加量

D．物体动能的增加量加上克服重力所做的功

答案

BD

题目分析：在升降机加速上升的过程中,地面提供的支持力做正功，等于重力势能以及动能增加量，即B正确。由于重力势能增加量大小就等于克服重力做功的值，所以D正确。

点评：本题考查了结合能量守恒定律判断物体能量守恒。要清楚克服重力做功、重力做功、机械能变化的区别与联系。

问答题 简答题

没有劲别的拳是什么拳？
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填空题

Seasick Try Controlling Your Breathing


If you get seasick easily, you may prepare for boat rides with pressure-point bracelets, ginger, or a prescription skin patch. (1) The technique presumably works because it helps control gravity sensors in the abdomen-a lesser-known input to our fine-tuned balance system.
(2) The inner ears sense motions of the head; the eyes see where the head is; and tiny sensory organs in muscles and tendons sense where the rest of the body is. More recently, researchers have realized that sensors in many other parts of the body also play a role: in the abdomen, the lower organs, and even blood vessels. (3) But if one or two don’t match up, the brain gets confused and we become nauseated.
Scientists knew the most sickening motions closely match the rate of natural breathing; they also knew that people naturally tend to breathe in time with a motion. (4)
Researchers from Imperial College London enlisted 26 volunteers to sit in a tilting, rocking flight simulator and coordinate their breathing in various ways with the motion. (5) The natural tendency was for volunteers to inhale on every backward tilt, in rhythm with the rocking. (6) They felt even better if they breathed slightly faster or slower than the cyclic heaving of the chair; using that technique, the time until onset of nausea was 50% longer than during normal breathing.
(7) Abdominal sensors are known to send motion signals to the brain more slowly than those in the inner ear because they’re farther away from the brain and because abdominal organs have more mass, which means they resist movement a tiny bit longer. (8) But if the diaphragm opposes gravity-induced stomach motions with controlled breaths, there is less sensory conflict and less nausea. "This technique is very good for mild everyday challenges," says medical research scientist Michael Gresty, a member of the study team. "it’s completely safe, and it’s not a drug."
A. But if the subjects exhaled on every backward tilt, they didn’t get sick as quickly.
B. As long as all of these sensors send matching signals to the brain, we feel oriented.
C. Now there’s one more remedy: timing your breathing to counteract the nauseating motion.
D. So why do these tactics work
E. The brain is traditionally thought to sense body position in three ways.
F. The time lag between the two types of sensors creates a mismatch that builds up in the brain and makes us gradually sicker, the researchers say.
G. The tests lasted up to 30 minutes, or until subjects felt moderately sick.
H. But no one had ever tested whether breathing out of time with a motion could prevent nausea.
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