Topic 4 - Energy

Question 1

Equations

Answer 1

Efficiency = useful energy output ÷ total energy output x 100%
Work done = force x distance moved
W = F x d
Gravitational potential energy = mass x gravitational field strength x height
GPE = m x g x h
Power = work done ÷ time taken
P = W ÷ t
OR
Power = energy transferred / time taken
P = E ÷ t
Kinetic energy = 1/2 x mass x speed^2
KE = 1/2 x m x v^2

Question 2

Energy stores

Answer 2

Chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear

Question 3

Energy transfers

Answer 3

Mechanically (physical), electrically, by heating, by radiation (light and sound)

Question 4

What is the energy transfers?

Answer 4

Using the principles of conservation of energy

Question 5

Work done is the same as…

Answer 5

Work done always equals to energy transfers

Question 6

Describe power

Answer 6

Power as the rate of transfers of energy or the rate of doing work

Question 7

Kinetic

Answer 7

Energy contained in moving object, e.g a bullet or a runner 

Question 8

Chemical

Answer 8

Energy stored in fuel (food, batteries etc.) which is released when a chemical reaction takes place, e.g coal, hamburger, cell

Question 9

Gravitational potential energy

Answer 9

Energy of an object due to its height above a surface , e.g a rollercoaster at the top of the track, a climber 

Question 10

Nuclear

Answer 10

Energy released from nuclear reactions , e.g nuclear power plant, the Sun

Question 11

Thermal

Answer 11

Energy stored in an object at a certain temperature (due to the random motion of its particles), e.g bonfire, radiator 

Question 12

Magnetic

Answer 12

The energy stored when repelling poles have been pushed closer together e.g magnets held close to each other

Question 13

Electrostatic

Answer 13

The energy stored when repelling charges have been moved closer together, e.g Van de Graff generator, thunderclouds

Question 14

Elastic

Answer 14

Energy stored in an object that is being stretched, squashed, e.g stretched bow, catapult 

Question 15

Mechanical work

Answer 15

A force moving an object through a distance, e.g windmill

Question 16

Electrical work

Answer 16

Charges moving due to a potential difference, e.g light bulb

Question 17

Heating

Answer 17

Due to temperature difference caused electrically or by chemical reaction,

Question 18

Radiation

Answer 18

Energy tranferred as a wave, eg light and infrared - light radiation and infrared radiation are emitted from the sun

Question 19

The principles of conservation energy

Answer 19

• energy can neither be created nor destroyed, it can only be stored or transferred.
• energy being wasted, means it has been transferred in a way that is no longer useful, usually via heating, increasing the thermal energy store of the surroundings.

Question 20

Sankey diagrams

Answer 20

These diagrams show how much energy is input into different devices and how much energy is transferred into different types of energy. It is possible to use the information in this diagram to work out the efficiency of the device.

Question 21

What is power?

Answer 21

Power is the rate of doing work – i.e. how much energy is transferred per second.

Question 22

Unit for power

Answer 22

Watt (One watt = 1 joule of energy transferred per second)

Question 23

What is work done?

Answer 23

The mechanical work done on an object is the energy transferred to it due to a force acting on the object and causing it to move.

Question 24

Unit for work done?

Answer 24

J/joules

Question 25

Describe Gravitational Potential Energy

Answer 25

Gravitational Potential Energy (GPE), depends on its position with respect to the surface of a massive object such as the Earth. The higher you raise an object, the more GPE it stores.

Question 26

Kinetic Energy depends…

Answer 26

Kinetic Energy (KE), depends on both its mass, AND how fast it is travelling.

Question 27

GPE to KE transfer (when object is dropped)

Answer 27

• object falls from a height, weight acts on it and hence work is done.
• there is a mechanical transfer, and GPE is transferred to KE in this way.
• This makes sense as we know that a falling object accelerates, so its KE must be increasing.
  GPE lost by the falling object = KE gained by it

Question 28

How does the height dropped from affect the efficiency of the bounce?

Answer 28

 As the drop height is increasing, the efficiency reduces at a increasing rate (we will see this better on a graph)