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Re: Test question



The answer to this question would normally be the water goes up,
assuming no pathological things. About the only time the water might
not go up is if the cup sinks and the original block is denser than
water (ironwood?). However, even then this is unlikely as ironwood is
only a little denser and the added block will likely compensate and
raise the water level.

Only students at the formal operational level of thinking are likely to
come up with such a pathological circumstance. Students at that level
are much more likely to do hypothetico-deductive reasoning and ask the
necessary "what if" questions. The average student is transitional and
the below average student is probably concrete operational so that both
are less likely to come up with the correct pathological assumptions.
If the question had been rephrased to say the cup continues to float,
then there would be only one possible right answer. Now of course some
students will assume the cup sinks and the original block floats and
then think that this makes the water go down.

One way of improving this question would be to make it rich context.
The actual densities and dimensions of both blocks, he cup's dimensions,
along with the information that the cup does not sink could be included.
This way the students have to understand what information is actually
relevant.

This test question is one that probably most students would get right as
stated. However there is a question which is far better in terms of
testing student understanding. That is the classic McDermott question
where you put several blocks all of different densities into a tank of
water. Assuming 5 blocks with 2 of them have density less than 1.0 and
3 with greater than 1 density. Students who do not really understand
will draw the two with lower density as floating at different heights,
and then the 3 others as suspended at various heights in the tank. They
might put the most dense one on the bottom.

Overall I would rank this question as fairly simple and slightly poorly
worded. It attempts to get at one concept which many students have
probably memorized, so I would not consider it to be a very good test of
understanding. However when combined with some other questions such as
the McDermott question and a possible rich context question it could be
part of a decent evaluation.

John M. Clement
Houston, TX



What is the answer to the following question
that appears on a recent examination in New York State.

A plastic cup containing a wood block is floating in a pan of water.
If another wood block is placed in the cup, what will happen to the
level
of the water in the pan?

A. It will go down
B. It will go up
c. It will stay the same