Physics

Physics

Problem

A 5.0 kg5.0\,\text{kg} crate is lifted vertically upward 2.0 m2.0\,\text{m} at constant speed. What is the change in the crate’s gravitational potential energy ΔUg\Delta U_g during the lift? (Use g=9.8 m/s2g = 9.8\,\text{m/s}^2.) a) +98 J+98\,\text{J} b) −98 J-98\,\text{J} c) +49 J+49\,\text{J} d) +196 J+196\,\text{J}
Intuitive explanation

Gravitational potential energy depends only on height, not on how fast or slow an object moves—so the constant speed is a red herring. The key insight is that ΔUg=mgΔh\Delta U_g = mg\Delta h: you just need the mass, gravitational field strength, and vertical displacement. Since the crate rises, its potential energy increases by the product of these three quantities.

Intuitive explanation

Gravitational potential energy depends only on height, not on how fast or slow an object moves—so the constant speed is a red herring. The key insight is that ΔUg=mgΔh\Delta U_g = mg\Delta h: you just need the mass, gravitational field strength, and vertical displacement. Since the crate rises, its potential energy increases by the product of these three quantities.

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