# Cloud physics help

Hi I have those 2 problems:

A typical cloud contains droplets of water with an average radius of .5 * 10^-4m.
how many droplets are needed for a cloud that provides a rainfall of .5 cm.
( the answer must be 1*10^21 droplets)

for this second problem I don't know how to find two equations:

A force F acting on a body of mass m a distance r from some origin has a magnitude of F=(A*m*exp(h*r))/r^4, where A and h are both constants.
Given that the force has dimensions kilogram-meter per seconds squared, what are the dimensions of both A and h.

Please can I have some help or suggestions for those problems?

Thank you very much

Related Introductory Physics Homework Help News on Phys.org
Tide
Homework Helper
(a) $$N = \frac{3 A h}{4 \pi r^3}$$

where A is the area to be covered, h = 0.5 cm is the depth and r is the radius of each drop.

(b) Hint: the argument of the exponential must be dimensionless - and - the dimensions of mA must be that of the force.

Last edited:
Yeah (b) shouldn't be a problem...

But what is (a)??

Granted I'm in high school but I've never encountered that kind of physics... where does it come from?

It is college physics freshman
but I am sure U can do it

I have no idea how Tide find the solution for the first problem ( N=....)
I will try to work on it but if I don't find something I will ask him how he did it.
Thanks

HiPPiE said:
Yeah (b) shouldn't be a problem...

But what is (a)??

Granted I'm in high school but I've never encountered that kind of physics... where does it come from?

Tide