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Re: Questions that lack sufficient information



At 10:38 AM 9/24/02, Gary Turner, you wrote:
I offer help through askme.com and have been quite surprised at the number
of badly worded questions that come through, mostly from math.com users.
These questions usually have vital pieces of information missing.

I was wondering if any others on the list had noticed similar problems. Do
these errors originate from the students submitting the questions, or are
they a result of poorly worded questions from the start? Does anyone know
where math.com gets their questions?

For example - a question I received today

A fire helicopter carries a 589 kg bucket of water at the end of a 17.1 m
long cable. Flying back from a fire at a constant speed of 39.7 m/s, the
cable makes an angle of 45.9 deg with respect to the vertical. Determine the
force of air resistance on the bucket.

This may seem a little picky, but there is no information about the
direction of flight. If you assume that constant speed really means
constant velocity, you still need the direction of flight (angle from the
vertical) to obtain the direction of the air resistance force.


If one chooses to plug numbers into the usual formula for
Drag Force = 1/2 rho v^2 A Cd

one tends to assume standard atmosphere
straight and level flight
and above all, an empty water bucket.

This leaves one to suppose plausible values for both the size (A)
and the weight of the cable and water vessel, not to mention a
sensible Cd for the ensemble.

This poses a certain 'real-world' uncertainty to the question,
I agree.


Brian Whatcott
Altus OK Eureka!