Edexcel iGCSE Physics -4.15 Conservation of Energy in Mechanical Systems- Study Notes- New Syllabus
Edexcel iGCSE Physics -4.15 Conservation of Energy in Mechanical Systems- Study Notes- New syllabus
Edexcel iGCSE Physics -4.15 Conservation of Energy in Mechanical Systems- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.
Key Concepts:
4.15 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work
Link Between Gravitational Potential Energy, Kinetic Energy and Work Done
The principle of conservation of energy states that energy cannot be created or destroyed; it can only be transferred from one form to another.
This principle creates a direct link between gravitational potential energy, kinetic energy, and work done.
Energy Changes When an Object Falls
- An object raised above the ground has gravitational potential energy.
- As it falls, gravitational potential energy decreases.
- The lost gravitational potential energy is transferred into kinetic energy.
- If air resistance is negligible, total energy remains constant.
Loss of GPE = Gain in KE
Role of Work Done
When a force causes an object to move, work is done.
- Work done against gravity increases gravitational potential energy.
- Work done by gravity increases kinetic energy.
- Work done = energy transferred.
This means that work links forces to energy changes.
Key Relationships Used
Gravitational potential energy:
\( \mathrm{E_p = mgh} \)
Kinetic energy:
\( \mathrm{E_k = \dfrac{1}{2}mv^2} \)
Work done:
\( \mathrm{W = F \times s} \)
All three quantities are measured in joules (J).
Energy Transfer in Real Situations
- Falling objects: GPE → KE
- Lifting objects: work done → GPE
- Braking vehicles: KE → thermal energy (work done by friction)
If friction or air resistance is present, some energy is transferred to the thermal store, but total energy is still conserved.
Key Idea
- Energy is conserved at all times.
- Gravitational potential energy, kinetic energy and work are directly linked.
- Work done explains how energy is transferred.
Important Points to Remember
- Energy lost from one store equals energy gained by others.
- Ignoring air resistance simplifies calculations.
- Always use SI units.
Example
A ball of mass \( \mathrm{2.0\ kg} \) is dropped from a height of \( \mathrm{10\ m} \).
Calculate the speed of the ball just before it hits the ground. (Take \( \mathrm{g = 10\ N/kg} \). Ignore air resistance.)
▶️ Answer / Explanation
Initial gravitational potential energy:
\( \mathrm{E_p = mgh = 2.0 \times 10 \times 10 = 200\ J} \)
By conservation of energy:
\( \mathrm{E_k = 200\ J} \)
Use:
\( \mathrm{E_k = \dfrac{1}{2}mv^2} \)
\( \mathrm{200 = \dfrac{1}{2} \times 2.0 \times v^2} \)
\( \mathrm{v^2 = 200} \)
\( \mathrm{v = 14\ m/s\ (approx.)} \)
Example
A student lifts a \( \mathrm{5.0\ kg} \) box vertically through a height of \( \mathrm{2.0\ m} \).
(a) Calculate the work done by the student. (b) State the energy change that occurs.
▶️ Answer / Explanation
(a)
\( \mathrm{W = mgh = 5.0 \times 10 \times 2.0 = 100\ J} \)
(b)
The work done by the student is transferred into gravitational potential energy of the box.