Answer
$$
\Delta U=-2.9 \times 10^{3} \mathrm{J} \text { . }
$$
Work Step by Step
Substituting the values given, the change in gravitational potential energy is
$$
\Delta U=U_{f}-U_{i}=-m g L$$$$=-(25 \mathrm{kg})\left(9.8 \mathrm{m} / \mathrm{s}^{2}\right)(12 \mathrm{m})$$$$=-2.9 \times 10^{3} \mathrm{J} \text { . }
$$
