Heh, this is a very easy problem dude.

Alright, here it is:

Area of a Cone = (1/3)*(PI)*(r^2)*(h)
Since r = h, Area = (1/3)*(PI)*(r^3)
Now, we know that (1/3)*(PI)*(r^3) = 1000
This is simplified to:
(PI)*(r^3) = 3000
(r^3) = (3000/PI)
r = Cubed root of (3000/PI), which = 9.847 (approximately)

Ok, now that we have that part solved, we find out the rate. It goes in at 10 cubic feet per minute, so after 1000 cubic feet is down, 100 minutes have passed.

Therefore, when the pile is at 9.847 feet high, 100 minutes have passed, and (9.847/100) = 0.09847 feet per minute.

That is the answer you were looking for, no?