Gravitational PE & conservation of energy
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Flip to reveal answersDefine gravitational potential energy (PE).
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All 12 Flashcards — Gravitational PE & conservation of energy
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Question
Define gravitational potential energy (PE).
Answer
The energy an object has **because of its height** in a gravitational field. It increases when the object is raised.
Question
Define kinetic energy (KE).
Answer
The energy an object has **because of its motion**. The faster it moves, the more KE it has.
Question
Formula for the change in gravitational PE?
Answer
$\Delta E_p = mg\Delta h$ — mass × gravitational field strength × change in height. (Given in the data booklet.)
Question
Formula for kinetic energy?
Answer
$E_k = \tfrac{1}{2}mv^{2}$ — half × mass × speed². (Given in the data booklet.)
Question
What does 'conservation of mechanical energy' mean for a falling body?
Answer
With no air resistance, **PE + KE stays constant**: the PE lost equals the KE gained.
Question
Equation linking PE lost to KE gained as a body falls?
Answer
$mg\Delta h = \tfrac{1}{2}mv^{2}$ — set the PE lost equal to the KE gained.
Question
At the top of a fall, how is the energy split?
Answer
**All PE, no KE** — it is at maximum height and not yet moving.
Question
At the bottom of a fall, how is the energy split?
Answer
**All KE, no PE** (taking the bottom as the reference height) — all the PE has converted to KE.
Question
Does a falling object's landing speed depend on its mass?
Answer
**No** — in mgΔh = ½mv² the mass cancels, so heavy and light objects reach the same speed (no air resistance).
Question
A stone falls a quarter of the way down. What fraction of its starting PE is now KE?
Answer
**A quarter** — KE gained = PE lost, so the fraction of height fallen = the fraction now KE.
Question
Where in a fall is PE equal to KE?
Answer
**Half-way down** — there it has lost half its PE, which has become KE, so PE = KE.
Question
What is the unit of energy?
Answer
The **joule (J)**. PE and KE are both measured in joules.
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