how many RPM are required to attain 1g with a radius of 840 feet

Answer 1

acceleration, a = rω² ft/s²
g=32.2 ft/s²
1 RPM = 2π rad/60 s
=π/30 rad/s

Let x=RPM required, then
ω=πx/30 rad/s
You need
g=rω²=r(πx/30)²

Solve for x.