If you, for example, poured it onto a wide cup with a volume equal to the total volume of the sand particles, the sand would not spread out to fill the container but would bunch up together in the middle.
You have three known variables:
Acceleration -

Time -

Initial Velocity -

For the first part of your question:

For the second part of your question:

This still needs to be converted to m/h:
a = ( V2 - V1)/( t2 - t1)
3.2 = ( 23.5m/s - 15.2m/s)/(t - 0)
3.2m/s = 8.3/t
t(3.2) = 8.3
t = 8.3/3.2
t = 2.59 seconds
True . this is called a complex substance
The question extends beyond what I already know.
The question makes me curious.