Two students discuss using to compute the change in gravitational potential energy…
PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two students discuss using U=mgh to compute the change in gravitational potential energy ΔU when a 5kg package is lifted a height h above Earth’s surface.
• Student 1: “The expression is always exact because g is a constant.”
• Student 2: “The expression slightly overestimates the true ΔU, and the percent error grows with h.”
Which statement correctly evaluates the students’ claims?
(a) Only Student 1 is correct; the variation in g with altitude is negligible, so mgh gives the exact ΔU at all heights.
(b) Only Student 2 is correct; mgh underestimates ΔU because g gets smaller with altitude, and the percent error increases with height.
(c) Only Student 2 is correct; mgh overestimates ΔU and the percent error increases with altitude.
(d) Neither student is correct; mgh underestimates ΔU because g increases with altitude beyond the surface.