I just encountered the following two homework problems while reading the
Newton's-second-law portion of a grade 9-12 physical science text[1] known
to be in current use in California and probably in other places. The same
implicit misconception appears in both problems, but for your reading
pleasure (?), I have reproduced the text of both problems verbatim below,
just to show you how hard the publishers' hack authors will work to
contrive what appear to be "new" problem types that are really no different
from each other. The two problems both appear on the same page of the
textbook (thankfully, in an appendix, not the main text).
1. "A peach falls from a tree with an acceleration of 9.8 m/s^2 downward.
The peach has a mass of 7.4 g. [Editorial comment: not a very big peach?
But wait; here comes the good part!] With what force does the peach strike
the ground?"
2. "A person steps off a diving board and falls into a pool with an
acceleration of 9.8 m/s^2, which causes the person to hit the water with a
force of 637 N. What is the mass of the person?"
Apparently neither the height of fall nor the duration of impact have any
effect on the results. I'll try to inform the publisher, but I have serious
doubt that this will accomplish anything.
--MB
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[1] Dobson, K., J. Holman, and M. Roberts, Holt Science Spectrum. Holt,
Rinehart, and Winston (2001), p. 747.