Re: [Phys-l] [ncnaapt] New Physics CST Questions Released!

["John Clement" <clement@hal-pc.org>]

Number 4 is a very poor picture because it looks like both show the effects
of air resistance, and the left hand picture seems to show a constant
acceleration, but with evident effects of air resistance, it should show
decreasing acceleration as the resistance increases.  Air resistance is the
only obvious answer, but the pictures are extremely poor.

Many of the later questions are straightforward and one is almost straight
from the FCI.  However the one on the difference between theory, conclusion,
and hypothesis is very bad.  The standards statements are also pretty poor.

John M. Clement
Houston, TX

> I'm uncomfortable with all of the questions on the first page. I'll look
> at
> the other questions when I have time. But here are some comments on the
> first 4 questions.
>
> 1) The phrase "most easily" bothers me. I typically make plots using a
> computer program, and I am very comfortable inputting data into a
> spreadsheet or a database.
>
> 2) What does "real-time" mean in this context? In fact, I can make graphs
> of
> displacement vs. time and velocity vs. time using all the tools provided.
> And further, a typical motion detector directly measures position vs. time
> and _calculates_ velocity vs. time. Also, lots of students do video
> analysis. What about students who have never used these particular
> measuring
> devices?
>
> 3) I'm literally aghast that the answer is "human error". Sorry that I
> don't
> have anything more constructive to add, but I really dislike this answer.
>
> 4) Answer choices A and C are _both_ valid. From the image, I conclude
> that
> A accelerates downward while B moves at nearly zero acceleration. If the
> air
> resistance of A is smaller than its weight, it will accelerate downward.
> If
> the mass (and thus weight) of the object is larger than the air resistance
> for the period pictured, the overall acceleration of the object would be
> also be downward.