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I can't help but wonder if you reproduced it accurately.
On Sun, 16 Sep 2001, Ludwik Kowalski wrote:
In my opinion problem 2.49 from Serway book (see below)
is poorly formulated. Why do they distract student with "the
driver of the car?" He is only an observer. Why does he
"slam on the brake?"
...
"The driver of a car slams on the brakes as a truck
approaches the car head-on while slowing uniformly
with acceleration -5.6 m/s^2. The driver of the car is
frozen with horror for 4.2 s while the truck makes
skid marks 62.4 m long. With what speed does the
truck strike the car?"
It's worse than that. I can't begin to make sense of this problem
statement and since both the truck and the car are evidently
moving toward each other AND decelerating, it doesn't come close
to providing enough information. I've seen some bad problem
statements before, but this one may take the cake. I can't help
but wonder if you reproduced it accurately.
In my Serway (PSE, 5th Edition) there is a very similar problem
(2.32) that is easily interpreted (sans the usual obvious targets
for nitpicking) and solved. It reads:
"The driver of a car slams on the brakes when he sees a tree
blocking the road. The car slows uniformly with an acceleration
of -5.60 m/s^2 for 4.20 s, making straight skid marks 62.4 m long
ending at the tree. With what speed does the car then strike the
tree?"
John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm