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Grains of fine sand are approximately sphere of an average radius of of 50 ìm are made of silicon dioxide. A solid cube of this material with a volume of 1m3 has a mass of 2600kg.

Question:

What mass of sand grains would have a total surface area (the total area of all the individual grains) equal to the surface area of a cube 1.1 meters on an edge?

Ok. I figured out the surface area of the cube by taking 1.1m*1.1m*1.1m*6= 7.986m^3

I figured out the surface area of a grain of sand by first converting micrometers into meters, and then plugging that number into the surface area forumula for a sphere.

SA of sphere= 4*pi*(50*10^-6m)^2= 3.14E-8.

Now, somehow the SA of a cube and SA of the grain are related, but I can't get the answer to be accepted by the online homework system. Any ideas?