Which statement about the signs of $v$ and $v_0$ in vertical motion is correct?
AThey are always positive because speed is positive.
BThey are always negative during free fall.
CTheir signs are determined by their directions relative to the chosen $+y$ axis.
DTheir signs depend only on the magnitude of $g$.
Answer & Solution
Correct answer: C. Their signs are determined by their directions relative to the chosen $+y$ axis.
Velocity is a vector quantity, so its sign depends on the coordinate system. In vertical motion, $v$ and $v_0$ are positive or negative according to whether they point along or opposite to the chosen positive $y$ direction.
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