Work and power

Question 1

What is work done, and what is its equation?

Answer 1

• Work is done when a force moves an object in the direction of the force.
• The equation for work done is: W = F × d
  
  • W = work done (Joules, J)
  • F = force applied (Newtons, N)
  • d = distance moved in the direction of the force (meters, m)
• Work is only done if there is movement in the direction of the applied force.

Question 2

What is the relationship between work done and energy transferred?

Answer 2

• Work done on an object is equal to the energy transferred to that object.
• When a force moves an object, it gives the object kinetic energy.
• This principle follows the conservation of energy.

Question 3

What is gravitational potential energy (GPE), and what is its equation?

Answer 3

• GPE is the energy stored in an object due to its height above the ground.
• The equation for GPE is: GPE = m × g × h
  
  • m = mass (kg)
  • g = gravitational field strength (N/kg, typically 9.8 N/kg on Earth)
  • h = height (m)
• The greater the height and mass, the more gravitational potential energy an object has.

Question 4

What is kinetic energy (KE), and what is its equation?

Answer 4

• Kinetic energy is the energy an object has due to its motion.
• The equation for KE is: KE = ½ m v²
  
  • m = mass (kg)
  • v = speed (m/s)
• The faster an object moves or the greater its mass, the more kinetic energy it has.

Question 5

How does the conservation of energy link GPE, KE, and work?

Answer 5

• Energy cannot be created or destroyed, only transferred.
• When an object is lifted, work is done against gravity, converting kinetic energy into gravitational potential energy (GPE).
• When the object is released, GPE is converted back into KE as it falls.
• As the object falls, GPE decreases while KE increases, keeping the total energy constant.
• If air resistance is negligible, all the lost GPE is converted into KE.
• If friction or air resistance is present, some energy is lost as thermal energy due to work done against resistive forces.
• Example: A roller coaster gains GPE when lifted to a height, then converts it into KE when descending.
• In a vacuum, where there is no air resistance, all objects fall at the same rate, showing perfect GPE to KE conversion.

Question 6

What is power, and what is its equation?

Answer 6

• Power is the rate of energy transfer or work done per unit time.
• The equation for power is: P = W / t
  
  • P = power (Watts, W)
  • W = work done (Joules, J)
  • t = time taken (seconds, s)
• The greater the power, the faster work is done.