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We are given that the solids are made from the same material, which means they have the same density.

 

Since   mass   =   density * volume

 

massA / massB   =   (densityA * volumeA) / (densityB * volumeB)

                                                                                                           densityA = densityB   so we can cancel them out

massA / massB   =   volumeA / volumeB

 

So here we have shown that the ratio of the masses is equal to the ratio of their volumes.

 

Now we need to be careful and remember that the ratio of their volumes is not equal to the ratio of their surface areas.

 

The ratio of their volumes is equal to the ratio of their surface areas raised to the power of 3/2

 

(See https://www.onlinemathlearning.com/similarity-area-volume.html )

 

volumeA  / volumeB   =   ( SAA / SAB )3/2

                                                                    Now we can replace   volumeA / volumeB   with   massA / massB

massA  / massB   =   ( SAA / SAB )3/2

                                                                    Now let's plug in what we know for values of  massB ,  SAA ,  and  SAB

massA / 6912   =   ( 28 / 40.32 )3/2

                                                                    Multiply both sides by  6912  and simplify.

massA   =   6912 * ( 28 / 40.32 )3/2

 

massA   =   4000            and that is in grams

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Sep 17, 2020
 #3
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+1
Sep 17, 2020
Sep 16, 2020
 #1
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Sep 16, 2020

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