Energy Transfers

Question 1

Define the law of conservation of energy

Answer 1

Energy can be transferred usefully, sorted or dissipated but can’t be created or destroyed

Question 2

What happens in a closed system

Answer 2

No energy can enter or leave the system

Question 3

Effect of friction

Answer 3

Causes energy to be transferred to thermal energy
= less useful
= energy has been dissipated

Question 4

How to reduce unwanted energy transfers on a pendulum

Answer 4

Reduce friction
- use lubricant on fixed point
- remove air particles from around pendulum

Question 5

Describe energy systems of bungee jumper

Answer 5

• gravitational potential energy at start
• as falls energy transferred to kinetic energy store
• as rope starts to tighten kinetic energy store at its maximum
• when rope fully extended kinetic energy is zero
  = jumper not moving
• all energy transferred to elastic potential energy store

Question 6

What happens when bungee rope recoils

Answer 6

• energy transferred from elastic potential energy store back to kinetic energy store
• during ascent kinetic goes back to gravitational energy store
• at top of ascent all energy is in gravitational potential energy store

Question 7

Key point of bungee jump

Answer 7

Jumper never returns back to original shape
= energy is dissipated as thermal energy
= due to friction with air particles
Or
= due to stretching effects in bungee rope which isn’t fully elastic

Question 8

Define direct potential difference

Answer 8

Polarity doesn’t change