Calculating efficiency (in terms of useful energy transferred) | Combined science

Starter quiz

Which of the following energy stores does friction transfer energy into?
- chemical store
- gravitational store
- kinetic store
- thermal store ✓
Why does a hot cup of tea cool down?
- All of its energy is used up.
- All of its energy is transferred to the surroundings.
- Some of its energy is used up.
- Some of its energy is transferred to the surroundings. ✓
Why is the rebound height of a ball not the same as the height that it was dropped from?
- Earth's gravitational force is pulling the ball downwards.
- The normal reaction force from the ground is less than the gravitational force.
- Pushing air out of the way uses up some of the ball's energy.
- Pushing air out of the way transfers some energy to the air particles. ✓
The law of conservation of energy states that energy cannot be created or ...
- 'destroyed' ✓
Match the values on the left to the equivalent values on the right.
- 1.5 kW
  
  ⇔
  
  1500 W ✓
- 3400 J
  
  ⇔
  
  3.4 kJ ✓
- 0.34 kJ
  
  ⇔
  
  340 J ✓
- 15 W
  
  ⇔
  
  0.015 kW ✓
Which of the following statements explains why an electric heater can be considered to be 100% efficient?
- An electric heater transfers no energy to the surroundings.
- An electric heater transfers all energy usefully into thermal stores. ✓
- An electric heater has a low power input.
- An electric heater has a high power input.