A large hollow ball of outer radius R₁ was put into space. Its inner radius is R₂. The shell of the hollow ball of thickness R₁-R₂ is uniform in mass distribution and has a total mass of m. If another mass m' was placed at a distance of R (R > R1) away from the center of the hollow ball, calculate the gravitational potential energy of this mass m'.

• A. $-\frac{Gm}{R}$
• B. $-\frac{Gm^{\prime}}{R}$
• C. $-\frac{G\left(m^{\prime}+m\right)}{R}$
• D. $-\frac{Gmm^{\prime}}{R}$

Answer: (D)