- #1

RayDonaldPratt

- 6

- 9

I am also told that this right cylinder has a mass of 49 grams, and I am told that the "density" is the mass (49 g) divided by the volume (11,960.69354 mm^3), which is .004096752402 g / mm^3 (before rounding).

My first question, or request for affirmation, is that the "49" grams reduces the number of significant digits in the final result to two digits, true?

I am then asked to express (convert) this density ratio into metric tonnes per cubic meter (Tn / m^3). And, I am told that a metric ton is 1,000 kilograms, or, as it were, 1,000 x 1,000 grams. That would be a Mg (Mega-gram). However, some online calculators that I have looked at for converting grams per cubic millimeter to metric tonnes per cubic meter would simply multiply 49 grams from above by 1,000, i.e., 49,000 tonnes per cubic meter. Right or wrong, the math does not make sense to me.

I assume that 1,000 cubic millimeters is 1 cubic meter. And, raising 49 grams proportionately would give me 49,000 grams, or, 49 kilograms. So, raising 49 kilograms to a metric tonne without proportionately changing from cubic meters would move the decimal place back three spaces to .049 metric tonnes per cubic meter.

With two significant digits, the answer after rounding would be .05 metric tonnes per m^3, but that answer has been marked wrong. I will try again with the answer of .049, but if that fails (it will be my fourth attempt), I will post this question to the Internet and ask how to correctly solve this problem. I am taking a Coursera MOOC about physics solely for my personal use. (I want to actually use math and physics to solve a more complex problem that I am personally interested in solving, and I am therefore more interested in understanding all the math and physics than in getting a passing grade with missed answers.)

Where and why does my thinking go wrong?