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Re: Test question



As usual, Mark's comments are EXCELLENT! However, the
plastic cups that I have available at home do sink
below the surface when they are full of water.
So let me ask again.... seriously,

Assume that a plastic cup and very small block of wood
inside are just floating on the surface of water in a large jar.
The density of the plastic cup is greater than the density
of the water and the rim of the plastic cup is only one
"RCH" above the surface with the rest of the plastic cup
below the surface.

When a second small block of wood is added, its weight
is just large enough to sink the plastic cup.

Will the level of the water in the large jar rise, sink,
or remain the same after the cup sinks to the bottom of the jar?

Herb
(For those who are unfamiliar with the term "RCH", ask any of
your engineering friends for help!)

On Wed, 04 Jun 2003 17:40:46 +0200 Mark Sylvester <msylvest@XNET.IT>
writes:
Herb,

Normal assumptions: I don't see how the cup can sink, assuming that
the plastic cup indeed has negligible weight. If the wooden blocks
float
when put directly in the water, and they fit inside the cup (it does
say
"another block is placed *inside* the cup"), then the cup cannot
sink.

Now if you cheat and *push* the cup down and make it sink, then the
water level will be the same before and after the sinking operation
since
the displaced water will in both cases be just what's needed to support

just the blocks (still assuming cup of negligible weight).

But this goes some way from the question, which asks what happens
*when you
add another block*. The water goes up, whether you sink the cup or
not.

Mark


At 10:37 04/06/03 -0400, Herbert H Gottlieb wrote:
I agree that your question (below) is a lot more interesting
than my origin question. However, I have still not received
a good answer to my original question.

Herb


On Wed, 04 Jun 2003 06:53:56 -0700 John Barrer <forcejb@YAHOO.COM>
writes:
I believe a more interesting question is:

Given the initial water level of the cup/2 block/pan
of water system (which is higher than with only one
block in the cup), what happens to the water level if
one block is removed from the cup and placed directly
in the water? Answer for two cases: one in which the
block floats partially submerged, the other in which
the block sinks to the bottom. John Barrere

--- Herbert H Gottlieb <herbgottlieb@JUNO.COM> wrote:
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


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Mark Sylvester
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Duino Trieste Italy