Q1. During free fall (ignoring air resistance), just before an object hits the ground, how are its potential energy and kinetic energy related?
- (a) Potential energy is maximum, kinetic energy is minimum
- (b) Potential energy is minimum, kinetic energy is maximum
- (c) Both kinetic and potential energies are zero
- (d) Some energy is lost due to conversion
Answer & solution
Answer: (b) Potential energy is minimum, kinetic energy is maximum
During free fall, total mechanical energy (potential energy + kinetic energy) is conserved (ignoring air resistance). As an object falls, its height decreases — so its gravitational potential energy (PE = mgh ) continuously decreases. Simultaneously, its velocity increases, so its kinetic energy (KE = ½mv²) continuously increases. Just before hitting the ground, height is nearly zero → PE is minimum (nearly zero), while velocity is maximum → KE is maximum. All of the initial PE has been converted to KE.
Option (a) Potential energy is maximum, kinetic energy is minimum — Incorrect: This describes the initial state (before falling), not just before impact.
Option (c) Both KE and PE are zero — Incorrect: Just before impact, velocity is maximum so KE is maximum; PE is near zero but KE is not zero.
Option (d) Some energy is lost due to conversion — Incorrect: In ideal free fall (no air resistance), energy is conserved; no energy is lost.