Work and Energy

Darwin G.

Q: What are the two factors required for work to be done?

• A: A force applied and a displacement.

Q: What is the SI unit of work?

• A: Joule (J).

Q: In which cases is work positive, negative, or zero?

• A:

  • Positive work: Force and displacement in the same direction.

  • Negative work: Force and displacement in opposite directions.

  • Zero work: No displacement or force perpendicular to displacement.

Q: How is work calculated when force is constant?

1. A: W=F⋅d⋅cos⁡θ, where F is force, d is displacement, and ⁡θ is the angle between them.

Q: What is the difference between work done at a constant force and work done at a variable force?

• A:

  • Constant force: The force remains the same throughout.

  • Variable force: The force changes with time or position (e.g., a spring).

Q: How does friction affect work?

A: Work done by friction is always negative because it opposes motion.

Q: What is the definition of energy in physics?

• A: Energy is the ability to produce a change in itself or the world around it.

Q: What is the work-energy theorem?

7. A: The work done on a system is equal to the change in its kinetic energy:
   W=ΔKE

Q: What is kinetic energy and its formula?

A: Energy of motion. Formula:
KE=1/2mv^2, where m is mass and v is velocity.

Q: What is potential energy?

A: Energy stored in an object due to its position or configuration.

Q: What is the formula for gravitational potential energy?

9. A: GPE=mgh, where m is mass, g is acceleration due to gravity, and h is height.

Q: What is Hooke’s Law?

A: F=kx, where F is force, k is the spring constant, and x is displacement.

Q: How is elastic potential energy calculated?

A: EPE=1/2kx^2

Q: What does the Law of Conservation of Mechanical Energy state?

• A: The total mechanical energy (kinetic + potential) in a system remains constant if only conservative forces act on it.

Q: What happens when nonconservative forces (like friction) act?

14. A: Energy is lost as heat, sound, or other forms.