A particle of mass m is placed at the center of a hemispherical shell of radius R and mass density \sigma, where \sigma has dimensions of \mathrm{kg} / \mathrm{m}^{2}. The gravitational force of the shell on the particle is
Answer Choices
A. (1 / 3)(\pi G m \sigma)
B. (2 / 3)(\pi G m \sigma)
C. (1 / \sqrt{2})(\pi G m \sigma)
D. (3 / 4)(\pi G m \sigma)
E. \pi G m \sigma
