Q 11-07-015NEETJEE MainEAMCET 2012 (Engineering)Medium
The gravitational field in a region is given by $\vec{E} = (5\hat{i} + 12\hat{j})$ N/kg. If a particle of mass $2$ kg is moved from the origin to the point $(12\ \text{m}, 5\ \text{m})$ in this region, the change in the gravitational potential energy is
Answer: (A) $-240$ J
Concept. The field does work $m\vec E \cdot \vec s$; $\Delta U = -W$.
Step 1. Dot product. $5(12) + 12(5) = 120$ J/kg.
Step 2. Change. $\Delta U = -2 \times 120 = -240$ J.
Answer. $-240$ J (Option A).
Solution by Sreeraj P, M.Sc Physics