A2 Daily A Level Physics question
In a lab, a trolley attached to a horizontal spring oscillates with negligible friction. You pull it back farther so that the amplitude increases from 3.0 cm to 6.0 cm, with the same mass and spring. Which statement best describes the change in its maximum kinetic energy, and why?
Answer
The correct answer is B.
Correct: B — Increases by a factor of 4, because the total energy is proportional to amplitude squared. A — Confuses speed with energy: maximum speed doubles, but kinetic energy depends on speed squared, so it quadruples, not doubles. B — Correct: doubling amplitude makes energy (and thus maximum kinetic energy) four times larger. C — The period staying the same does not mean the energy is the same; energy depends on amplitude, not period, for the same system. D — Time spent near turning points does not reduce the maximum kinetic energy at the centre; with larger amplitude the maximum speed is higher, so maximum kinetic energy increases, not decreases.