# Pressure of falling sand

JSmith123

## Homework Statement

Grains of sand of mass 3.10 10-3 g each, fall from a height of 0.8 m on a sticky surface at a rate of 50 grains per second per cm^2. What pressure does this shower of sand exert on the surface, assuming that air resistance can be neglected?

P=F/A
F=ma=mv d/dt

## The Attempt at a Solution

So I understand I have to calculate the velocity and multiply that by the mass and number of grains. What I don't understand is the area. What is the area? Any help would be great.

cupid.callin
use F = dP/dt to find force due to 1 grain ..... multiply with total number of grains ..... and then divide the area on which this total force is acting .... you get pressure

JSmith123
use F = dP/dt to find force due to 1 grain ..... multiply with total number of grains ..... and then divide the area on which this total force is acting .... you get pressure

I see, but what is the area?

cupid.callin
from P = F/A you can see that P=F when area is 1m^2

and you can also find force in 1cm^2

so its easy to find force in 1m^2 also, right?

JSmith123
Oh jeez the area is just 1m^2? I can't believe I didn't notice that. Anyways, thanks for the help.