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A. On the force vs. acceleration graph at right:
1. What do the three different lines represent? 2. How is the slope of a line related to the object that produced that
line? 3. What is the interpretation of the slope of each line? 4. What does it mean for all the lines to go through the origin? What would it mean if someone had
drawn a line that started on a non-zero value on the horizontal axis? II. Pushed book
Using your hand to exert a horizontal force, you push a physics textbook across the floor at a steady pace.
The frictional force exerted by the floor on the book opposes its motion. Is the “push” force exerted by
your hand greater than, less than, or equal to that frictional force?
A. What’s an incorrect, but reasonable, answer that someone like your (perhaps hypothetical) roommate,
a humanities major, might give? Explain what that person might be thinking and why it would be
reasonable even though incorrect. © University of Maryland Physics Education Research Group, Fall 2006. HW4-1 101115
B. Now you answer the question, and explain your reasoning. C. Is there a way to reconcile the reasonable-but-incorrect idea underlying your roommate’s reasoning
with your own reasoning in this case? Or would you just have to tell the roommate to accept your
reasoning because experiments support it? (Hint: How could your roommate refine his or her
intuition to be consistent with your reasoning?) D. In almost every tutorial and homework that you’ve done (including the question above!), we’ve had
you spend a lot of time thinking about mistaken reasoning—your own mistakes and even other
people’s mistakes. What do you see as the point, if any, of focusing on mistakes? (We’ve asked this
before, but not on an assignment you handed in., and we want to see what you think.) Please be
honest; write what you think, not what your professor thinks. You’ll get full credit for completing
this part-D sincerely, no matter what you say. © University of Maryland Physics Education Research Group, Fall 2006. HW4-2 ...
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