Competition Problem 1 English Version

 

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Scoring Rubric:

1. SCORING RUBRIC
There should be an explanation of why the process is controlled at first. This can be fairly sketchy, but it must be rational, and should mention the difference in heights between the columns. 1point

The next two points are concerned with the numerator and denominator of a = F/m. The students do not have to present it this way, so long as the following two elements appear.

  • After the water passes the bottom of the tube, the net force on the remaining water column increases due to loss of water at the top. They must recognize the diminishing role of gravity on this column. (Thus the numerator above increases.) It is OK if they are not too sure about what the pressure does as long as they do not make a claim that wildly diverges from the actual case (pressure does not change much). 1 point
  • The mass of the column decreases (so the denominator decreases). This must be a reference to the inertia of the column, and be easily distinguishable from the reduced weight which has been counted above. 1 point

    • The acceleration increases for two separate causes, and so increases faster than for either of the causes acting alone. Deciding this point from their writing  can be difficult. The test could be either a clear indication that they describe the acceleration as increasing nonlinearly (use judgment about their description) or that they have ascribed two distinct causes for the increase. 1 point

    The rapid change in the acceleration is hard to control. 1 point

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