The dwarf planet Ceres has a radius of $476\mathrm{km}$, a mass of $9.5\times {10}^{20}\mathrm{kg}$, and a free fall acceleration due to gravity of $0.28\mathrm{m}/{\mathrm{s}}^2$. What speed will a rock have if it is orbiting Ceres, right on the surface? Ceres has no atmosphere – so there are no issues with air resistance – but assume that there are no mountains or large boulders to impede the orbit.

• A. $130\mathrm{m}/\mathrm{s}$
• B. $560\mathrm{m}/\mathrm{s}$
• C. $780\mathrm{m}/\mathrm{s}$
• D. $1200\mathrm{m}/\mathrm{s}$
• E. $8000\mathrm{m}/\mathrm{s}$
• F. $370\mathrm{m}/\mathrm{s}$