Answer:
Volume of each grain of sand:

radius of the spherical grain is given,

The grains are made up of silicon dioxide.
The density is equal to 
Then, the mass of each grain is given by:

Answer:
B. 0.1 meters/second/second in the same direction of travel.
Explanation:
Acceleration is the rate of change of velocity. Acceleration is a vector quantity.
a=Δv/Δt
=(v₂-v₁)/(t₂-t₁)
v₁=4 m/s
v₂=6 m/s
t₁=0 s
t₂=20 s
a=(6m/s-4m/s)/(20s-0)
= 0.1 m/s² in the same direction of travel.
Therefore acceleration =0.1 meters/second/second in the same direction of travel.
"C) The movement of the gas particles keeps the balloon inflated" best describes the gas trapped in a sealed balloon, although the movement varies with the heat of the gas.