Fine grains of beach sand are assumed to be
spheres of radius 38.9 µm. These grains are
made of silicon dioxide which has a density of
2600 kg/m3
.
What is the mass of each grain of sand?
Answer in units of kg.

Question

anonymous · Answer

well mass = density * volume
and the volume of a sphere is $$Volume = (4/3)*\Pi*Radius ^{3}$$

anonymous · Answer

so $$Volume = (4/3)*\Pi*(38.9*10^{-6})^{3}$$$$Volume = 0.2465683979*10^{-12}  m ^{3}$$finally$$mass = 2600*0.2465683979*10^{-12} =0.641kg$$

anonymous · Answer

$$6.41∗10^{−10}kg$$
your last calculation is off by a factor of a billion

anonymous · Answer

6.41*1/10^10

anonymous · Answer

Consider a cube whose sides are 1.18 m long.
How many kg of sand would it take for the
total surface area of all the grains of sand to
equal the surface area of the cube?