Energy - AQA GCSE physics

How much energy is stored as a kinetic store when a toy rocket of mass 4kg

moves at 20 m/s?

• 30J

• 60J

• 600J

• 800J

Answer explanation

Kinetic energy = 1⁄2 x mass x velocity^2

which is 1⁄2 x 4 x 20^2 = 800 J

A torch transfers 300J of its chemical potential store in its cells to 120J of useful

energy. What is the efficiency?

• 0.4 J

• 0.48 J

• 0.6 J

• 2.5 J

Answer explanation

Efficiency = 120 J ÷ 300 J = 0.40

A ball is thrown upwards into the air until it reaches its maximum height. What are the changes in energy stores for this example from the instant

that the ball leaves the thrower’s hand?

• Kinetic energy will decrease, gravitational potential energy will increase

• Kinetic energy will increase, gravitational potential energy will increase

• Kinetic energy will decrease, thermal energy will decrease

• Gravitational energy will increase, thermal energy will decrease

Answer explanation

Gravitational force will decelerate the

ball as it goes up to its highest point

Which of the following statements about energy and power is correct?

• An energy transfer of 1 joule per second is equal to a power of 1 watt

• A joule is 1 watt per second

• Energy is measured in watts, W.

• Power (W) = energy (J) x time (s)

Answer explanation

An energy transfer of 1 joule per second is equal to a power of 1 watt

Which statement below about energy transfers is true?

• Energy can be transferred, created or destroyed

• The energy in a closed system is greater after a transfer than it was before the transfer

• Energy transfers usually occur so that no energy is wasted to the surroundings

• Energy can be usefully transferred and wasted but cannot be created or destroyed

Answer explanation

Conservation of energy - Energy can be usefully transferred and

wasted but it cannot be created or

destroyed

13 A lawnmower transfers 140W of every 250W of its input power to useful

energy. Which of the following rows is correct for this example?

• The efficiency of the lawnmower is 44% and 140W is wasted

• The efficiency of the lawnmower is 56% and 110W is wasted

• C The efficiency of the lawnmower is 56% and 140W is wasted

• The efficiency of the lawnmower is 178% and 110 W is wasted

Answer explanation

140 W ÷ 250 W = 0.56 = 56% which is the efficiency.

Power wasted per second is

250 W – 140 W = 110 W

Which of the following statements about the reliability of different energy

resources is true?

• Wave power is the most reliable of all the energy resources

• Tidal power is non-renewable and very reliable

• Wind and solar power are highly reliable renewable resources

• Coal and nuclear fuel are non-renewable and reliable sources of energy

Answer explanation

Coal and nuclear fuel are readily

available and do not depend on the

weather or other factors

Which of the statements below is correct about the environmental impact of

energy resources?

• Coal, oil and natural gas all give out large amounts of carbon dioxide when burned

• Nuclear fuel is a major contributor towards global warming.

• Hydroelectric dams and wind farms do not affect the habitats of plants and animals

• Wind farms are not considered to be a cause of visual pollution

Answer explanation

Fossil fuels contain large amounts of carbon and sulfur, which lead to global

warming and acid rain when burned.

Use the graph to decide which statement about the use of energy resources in

the USA since 1776 is correct.

• The USA uses mostly renewable energy resources

• The increase in the amount of petroleum used is not related to the growth in

  population since 1776

• Natural gas and coal are more commonly used compared with nuclear fuel

• The amount of natural gas used has remained constant since 1900

Answer explanation

Natural gas and coal are more commonly

used compared with nuclear fuel based on the values on the graph

How much energy is transferred by five 60W bulbs in 20 minutes?

• 30J

• 1200J

• 7200J

• 360,000J

Answer explanation

Energy transferred = power x time

Energy transferred = 5 x 60W x (20x60) s

Energy transferred = 360,000 J