So what you mean is, with the options "time, mass, neither", a unit that can quantify mass (like pound) but also something else (lbf -> force) should accept "neither"? Admittedly, you may have a point, since it can also be correct. But allowing "mass" as an answer for pound certainly is not incorrect in itself. The problem is that this common misconception about mass and weight, proportional in our surroundings and reference systems, only led to this trouble with the same name used for both. So I do not think that the quiz is inaccurate, rather that there would be more than one accurate way of implementing it. At the very least, comments as "pound is weight, not mass" are wrong, since they fail to see that there is also a pound describing mass.
@Jabob: it doesn't make a difference in the end (apart from rounding in the very last digits), since this is our classical frame of reference. Still, technically Jefe is correct: the acceleration by gravity originates from a force of attraction between two masses which is proportional to both of these masses. So if we treat Earth's mass as constant, the force on an object of mass 2 will be precisely double the force of an object of mass 1, but the force will have to accelerate an object of twice the weight, so the resulting acceleration will be the same. So the weight does factor in, but is cancelled out by mass, which is proportional to the weight. |
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