Two 25 kg balls are 3.0 m apart. Find the gravitational potential and field midway between them.

Step 1. Potential. $V = -2 \times 6.67 \times 10^{-11}\ \text{N m}^2/\text{kg}^2 \times \dfrac{25\ \text{kg}}{1.5\ \text{m}} = -2.22 \times 10^{-9}\ \text{J/kg}$.

Step 2. Field. Equal and opposite pulls cancel: $0$.

Step 3. Work. From $V$ to $0$: $1.0\ \text{kg} \times 2.22 \times 10^{-9}\ \text{J/kg} = 2.22 \times 10^{-9}\ \text{J}$.