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Analyse（Explain how you know where each of these points is.）
Before I did this experiment, I made a mark on the ramp. I did not released the car before it pass the mark. The graph started when the car pass the mark. So I started pushing the car before the “zero” and stopped pushing at “zero”. From the acceleration graph, the acceleration has changed at “2”. It caused by the direction of the net force has changed at that time. As we all know, the net force always against the object. So point “2” is the top. At point 4.2, the car stopped. So the point 4.2 is the end point.
（Explain the second question.）
The acceleration was different between it gone up and gone down. When it gone up, the acceleration was mg*sin(A)+ net force. When it gone down, the acceleration was mg*sin(A)- net force. So the absolute value of acceleration of gone up was larger than the one of gone down. Both the distance of gone up and gone down is same.
Technically, the acceleration is mg*sin(A) at that moment(stopped at the top). The graph did not show the acceleration at that moment.
When the cart was at the top, the velocity would be very close to zero and it also would be positive in the next instant. [(lim x→0+)x]
以上是我的物理作业，明天要上交。帮我看看有什么错误。谢谢！ |
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发表于 2009-9-30 23:48
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