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Re: [Phys-L] Freshman Physics

I appreciate all of the feedback. Just by way of further information:

1. All my quizzes of this kind (multi-step problems) are handed out in
class and returned to me in lab (in this case a Monday class and Wednesday
lab). This gives them time to think.

2. I never do problems/examples in class with numbers. I show them that
if you solve the block on an inclined plane connected to a block hanging
over a pulley, twice -- once moving up and once moving down the plane --
you've solved every blasted problem in the back of the chapter.

Let me give you my results...

The "house" problem --
10% failed the problem with no idea how to start.
1 student used Python to run a nested loop to try a range of velocities
with a range of angles! Very inventive.
2 students did a "worst case scenario" approach and did the huge angle
assumption and then just solved for a velocity that worked.
The remainder of them did the algebra, working their way through it,
although not without some math errors in some cases.

All in all, I was very happy with the work, inventiveness, and range of
approaches. I don't want them to think the real world is "plug and chug"
and want them to learn to think. I believe I got that. I would definitely
change the problem using some of John Denker's suggestions next time --
especially changing the house into a wall.

The "rope" problem --
Everyone could do the force diagram.
Some of them tried to simplify it by turning it into two masses connected
by a massless rope -- which doesn't work of course.
Of the ones who got the variable mass idea, only 43% of the class, the
solution they got was correct although some of them left the second part in
integral form because they couldn't integrate it.
I'll spend some time going over this one in class because they all deserve
to see the process. Because only 43% of the class could complete it, I'm
not going to count this one toward their grade.

I thank all of you for the feedback!
Peter


On Sat, Oct 15, 2022 at 11:18 AM Todd Pedlar via Phys-l <
phys-l@mail.phys-l.org> wrote:

I think the first problem is pretty difficult for a first year student on
an exam or quiz - homework, maybe, but in a timed setting I can't imagine
this going well for most. I'm not sure how you envisioned students doing
that problem, but I can imagine that most of the better students would
recognize that the required range of 80m gives them a handle on the
combination of v0^2 * sin(2*theta) and then use the requirement that
delta*y be greater than 35m at a distance of 25m from the launch point when
the ball reaches that point to write down an equation that relates the
angle and the speed. Then, in principle, they could sub in for the launch
speed and find an equation that gives a minimum angle.

Honestly I think the vast majority of students would be lost in the weeds
and not be able to foresee the path through the algebra to make the
necessary substitutions in an exam setting.

The second problem I definitely think would be beyond all but the best
students even in a homework setting. Never would I imagine putting that on
an exam for intro physics.


On Sat, Oct 15, 2022 at 9:26 AM Brian Whatcott <betwys1@sbcglobal.net>
wrote:

I attempted Peter's first problem. I did my best to be a lazy solver. I
wanted the general form of the equation of the parabola, using three
points
on the trajectory. I chose to use [0,0], [20,35], and [80,0] Notice
this
is a worst case for a very low pitch roof. I found the general form was
-7*x^2 +560*x -230*y = 0 using an online parabola calculator,

https://www.emathhelp.net/calculators/algebra-2/parabola-calculator/?type=d&p1x=0&p1y=0&p2x=20&p2y=35&p3x=80&p3y=0&dir=x
This provides about 5 meters headroom at the peak of the roof; a flight
time of 6.169 seconds (using Wolfram alpha at
https://www.wolframalpha.com/input?i=0+%3D+30.259*t+-+0.5*9.81*t%5E2
to solve the quadratic) at a launch velocity and angle of 32.93 m/s at
66.7 degrees.I expended two sheets of paper for working.
I have to suppose there is an easier way which eluded me.

On Friday, October 14, 2022 at 06:07:30 AM CDT, Anthony Lapinski via
Phys-l <phys-l@mail.phys-l.org> wrote:

Expecting too much? I don't know. Interesting problems? Well, we all
think
our (physics) problems are interesting! Useful problems? Maybe. I'm not
sure what the (science) backgrounds of your students are. I teach at a
private high school. Over the years I've had to make the problems
"easier"
(e.g., adding more parts to a problem). They still find them challenging.
The strong kids remain strong, but the weak kids are weaker. Plus there
is
much grade inflation, test corrections, cheating (?), etc. And social
media
and smartphones have made kids more distracted, less curious about
science,
less patient, lazier, less caring about academics, harder to teach.
Nobody's fault. It's the world they have/know, and it's only getting
worse.
Obviously a much bigger (and more important) discussion than the problems
you posed.

On Fri, Oct 14, 2022 at 6:32 AM Peter Schoch <pschoch@fandm.edu> wrote:

I teach at a community college. Due to rising tuition rates, our
physics
classes have grown, mostly with those students who want to go on to
engineering majors when they transfer. Because of the increase, I
can't
teach every section anymore and I hired an Adjunct who is a retired
high
school AP physics teacher.

After much discussion, he's convinced that I am asking too much of the
students! His contention is that the problems I make them do for
quizzes
and tests are too difficult for this level. For example, I just had
them
do the following 2 problems:

1. You are standing 20 meters from a building. The building is 10
meters
wide and 35 meters high. The second person is 50 meters from the other
side of the building. With what initial speed and launch angle should
a
ball be thrown to get to the second person.

HINT: The “peak” of the building (35 m) is located directly at the
midpoint of the building. To ensure that the ball clears the top of
the
building, its height above the ground should be no less than 35.1m at
this
point.

2. A uniform rope of length L has a mass M. It is stretched out
along a
table with a portion of the rope, x, hanging over the edge of the
table.
There
is a coefficient of friction, μ, between the rope and the table.

a. What fractional length of rope must be hanging off the table for it
to
begin to move?

b. If there is sufficient rope hanging off the table, what is the
functional form of its velocity as a function of x?

I thought they were interesting problems that would be useful to them.
He
is adamant that the problems are too complex for Freshman.

Which brings me to my question -- am I expecting too much from these
students when asking such questions?

Thanks,
Peter Schoch
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Todd K. Pedlar
Professor of Physics and Physics Department Head
Luther College, Decorah, IA
pedlto01@luther.edu
(563) 387-1628
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