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Richard Tarara wrote:_______________________________________________
Question 8 has a problem that we all have to be careful about. Since the
velocity is a vector quantity, and mathematically we consider negative
quantities to be less than positive quantities, none of the answers are
mathematically correct.
We agree that in general vector quantities cannot be considered positive
or negative, and that students are often confused by this. However, there
is a big fat exception for one-dimensional vectors. And since the item we
are discussing is explicitly one-dimensional, it beats this rap.
One-dimensional vectors are isomorphic to plain old numbers, and can be
considered positive, zero, or negative.
However, if one argues that a negative velocity IS
NOT 'less' than a positive velocity, just in a different direction,
There's no chance of that. Take a look at the number line. Negative
numbers *are* less than positive numbers. No choice.
.... The question SHOULD have asked about the speed of the ball
to eliminate this confusion.
Yup. BTW it's not a "confusion". It's a gross error. All four
choices are so grossly wrong that it is impossible to choose a "best"
answer ... except by assuming that the person who composed the question
doesn't know anything about physics. The question has very limited
value in assessing students' knowledge, and strongly negative value
in terms of teaching-via-the-exam.