Study Notes
In mechanics, energy, work, and power are fundamental concepts used to describe the motion and forces acting on objects. Work is done when a force causes an object to move, and energy is the capacity to do work.
- Work — the product of the force and the distance moved in the direction of the force. Example: A force of 40 N moves an object 20 m, work done is 800 J.
- Kinetic Energy — energy a body possesses due to its motion. Example: A 2 kg particle moving at 4 ms⁻¹ has kinetic energy.
- Gravitational Potential Energy — energy a body possesses due to its position in a gravitational field. Example: A mass raised to a height gains potential energy.
- Conservation of Energy — total energy in a closed system remains constant. Example: Potential energy converts to kinetic energy as an object falls.
- Power — the rate of doing work. Example: An engine doing 1000 J of work per second has a power of 1 kW.
Exam Tips
Key Definitions to Remember
- Work: Force times distance in the direction of the force
- Kinetic Energy: 0.5 times mass times velocity squared
- Gravitational Potential Energy: Mass times gravity times height
- Power: Work done per unit time
Common Confusions
- Mixing up units for work (Joules) and power (Watts)
- Confusing potential energy with kinetic energy
Typical Exam Questions
- What is the work done by a force of 10 N moving an object 5 m? Answer: 50 J
- How do you calculate the kinetic energy of a 3 kg object moving at 2 ms⁻¹? Answer: 6 J
- What is the power of an engine doing 2000 J of work in 2 seconds? Answer: 1000 W
What Examiners Usually Test
- Calculating work done by forces at angles
- Applying conservation of energy in problem-solving
- Understanding the relationship between power, force, and velocity