Conservation of energy

Question 1

State the law of the conservation of energy

Answer 1

Energy cannot be created or destroyed, only transferred

Question 2

Describe the energy transfer for a falling object

Answer 2

• An object starts with gravitational potential
  energy (GPE)
• As it falls, GPE is transferred to kinetic energy
• Some energy is dissipated to the surroundings
  as heat

Question 3

State the relationship between Gravitational potential energy (GPE) lost and kinetic energy (KE) gained for a falling object

Answer 3

GPE lost = KE gained

Question 4

Describe how to calculate efficiency

Answer 4

Efficiency (%) = (Useful energy output / Total energy outfit) x 100

Question 5

What is the equation for gravitational potential energy (GPE) ?

Answer 5

GPE (J) = Mass (kg) x height (m) x Gravitational field strength (N/Kg)

Question 6

What is the equation for kinetic energy?

Answer 6

• Kinetic energy (J) = 0.5 x mass (kg) x velocity (m/s) x
  velocity (m/s)
• KE = 1/2 mv^2

Question 7

Rearrange the equation for kinetic energy to calculate velocity

Answer 7

• KE / (0.5 x mass) = v^2

Question 8

How can we reduce unwanted energy transfers for moving objects

Answer 8

Reduce friction (e.g. add lubricant) to reduce thermal energy transfers