Then again, if you know of any state in the union that does better
for its mandated, statewide 9-12 physics tests and releases
questions, give us links!
The Assessment Review Panels have been dissolved due to budget
constraints until further notice. If you are disappointed with the
quality of the CST items now, it promises to get worse in the future.
More fodder for discussion boards!
Posted on PTSOS by Dean Baird:
The process by which an item makes it on to the CST is ... involved.
Add a few more steps for those that get released.
Items are developed by ETS and screened by the California Department
of Education and by its Assessment Review Panel. If that all goes
well, the item is field-tested. The item must perform well on a
series of psychometric measures. Most importantly, the item must be
neither too easy nor too hard, based on student performance on the
item. And the item must discriminate well. That is, students who
perform well on the test overall should perform well on the item. And
students who don't perform well on the test overall should perform
poorly on the item. There are always some items that "smart" kids get
wrong and "dumb" kids get right. Those items are rejected.
It is a rare item that, if presented to a room of 100 physics
teachers, would be met with universal approval.
The student in the diagram transitions from crouched to being in
flight. During that process, the scale reading will increase
momentarily and then drop off. Answer B really is the best of the
available choices. It is consistent with force-plate observations of
the actual event.
And the item performed well with students in terms of difficulty and
ability to discriminate. Students are unlikely to "overthink" items
they way physics teachers do by nature.
If you don't like the item, rest assured it will never appear on any
operational form for any future CST.
The Assessment Review Panels have been dissolved due to budget
constraints until further notice. If you are disappointed with the
quality of the CST items now, it promises to get worse in the future.
More fodder for discussion boards!
Then again, if you know of any state in the union that does better
for its mandated, statewide 9-12 physics tests and releases
questions, give us links!
--- In PTSOS@yahoogroups.com, Frank Lee <menkbiz@...> wrote:
>
> Like any physics teacher would be doing on Thanksgiving break, I
was looking over the physics released test questions. I came across
this one and found it confusing (equally confusing picture attached):
>
> A student in a lab experiment jumps upward
> off a common bathroom scale as the lab
> partner records the scale reading.
>
> What does the lab partner observe during the
> instant the student pushes off?
> A The scale reading will remain unchanged
> during the entire time the student is in contact
> with the scale.
> B The scale reading will increase momentarily
> then will decrease as the student is moving
> upward from the scale.
> C The scale reading will increase during the
> entire time the student is in contact with
> the scale.
> D The scale reading will decrease momentarily
> then will increase as the student is moving
> upward from the scale.
>
> Is this really a fair question to ask??? What assumptions are we
making? The picture shows two pictures: 1) Guy crouched on scale 2)
Guy in midair.
> I'm making the following assumptions: 1) We ignore the mechanism
of the scale and assume it displays the real-time force (and anyone
who has used a traditional analog bathroom scale knows that's not
true). I'm making this iffy assumption based on the iffy assumption
that whoever created this question has good enough judgment not to
assess a student on the mechanism of a bathroom scale on top of their
assessment of N2L/N3L. 2) Based on the picture, we're beginning our
measurement as the guy accelerates upward, NOT including his action
of lowering himself to a crouch 3) He accelerates upward at a
constant rate because non-constant acceleration isn't in the standards
>
> Using these assumptions, I'm modeling the person as an object
accelerating upward at a constant rate. Therefore, there is a
constant unbalanced force being exerted upward on him by his feet/
legs (N2L). (Wow, this is getting really complicated in my head... I
hope I'm not needlessly overcomplicating this.) Due to N3L, his body
is exerting a constant downward force on his feet/legs. His feet/legs
are still, meaning forces on them are balanced, meaning there's a
constant force upward on his feet from the scale. N3L now says that
constant force must also be exerted downwards by his feet on the
scale. Then I'm sure I'm making some reasonable simplification by
saying this is the force that the scale measures.
>
> Following this logic, I would say the scale measures a constant
force greater than the weight of the guy. Except that is not a
choice. Fine. The next closest answer is C, that the force is
constantly increasing, which would mean the guy's acceleration is
increasing. Still plausible.
>
> The answer is B.
>
> WTF.
>
> Frank
>