試題詳解

3. An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it, the spring is extended 5.0 cm from its relaxed length. A downward external force is now applied to the mass to extend the spring an additional 10 cm. While the spring is being extended by the force, the work done by the spring is about:
(A) -3.92 J
(B)-1.96 J
(C) 0 J
(D) 1.96 J
(E) 3.92 J.