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The preamble to the problem tries to get around issues of impulse applied
at
an instant, I think. I don't want to be too specific in an open forum, of
course, but do others think that the description before the figure deals
with the issue that Bill brought up?
On preview, I see that JD has brought up the similar point.
sincerely,
Krishna
Krishna Chowdary
Faculty, Math & Physics
The Evergreen State College
Olympia, WA 98505
On Sat, Feb 14, 2009 at 11:38 AM, Bill Nettles <bnettles@uu.edu> wrote:
John,is
That's what I thought, too, initially. Then I began thinking, "If this
an implusive force directed perpendicular to the instantaneous velocity,is
then it does zero work. That means the speed doesn't change, only the
direction." Am I missing something?
Thanks,
Bill
Assuming you have the same version, the answer to #9 from Mazur's book"John Clement" <clement@hal-pc.org> 2/13/2009 2:14 pm >>>
#5Mazur's
in the answer key. This is the question about the "speed" of the puck
after the kick.
The main problem is that Vk has not been defined in the version in
book, but it should be evident that this would be the velocity if theball
were not already moving. And both concepts give the same answer becausev0
is perp. To Vk. So the speed is greater than either V0 or Vk, but lessbut
than
the arithmetic sum of them. I would say it is testing vector addition,
that depends on the student understanding that the change in velocity Vkis
in the direction of the kick which is perpendicular to the initial5
velocity.
So there are actually 2 concepts in this question.
I would agree with Mazur's answer key, and his answers are numbered 1 to
rather than A to E.that
John M. Clement
Houston, TX
opinions
I'm trying to avoid "spoiling" the FCI answers, but I'd like some
on one of the questions and whether it should be included. Can we do
accelerationhere?#9.
I'm NOT INTERESTED in opinions on the FCI in general, just on question
I don't have the "official" answer sheet, but I'm not sure whether the
intent is to test vector addition or relative direction of
conceptand velocity. One would expect different answers depending on the
vectorbeing tested. The first time I read the test, I said "Oh, this is
_______________________________________________addition." But a closer look makes me think of "instantaneous"
perpendicular impulse.
What do you think is intended?
Bill
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