energy - forces doing work

Question 1

Describe the changes involved in the way energy is stored when systems change

Answer 1

• when a systme changes, ENERGY IS TRANSFERRED
• it can be trasnferred
  a) into or away from the system
  b) between different objects in the system
  c) between different types of energy stores

Question 2

how is some energy stored whenever a system changes

Answer 2

some energy is dissipated and stored in less useful ways

Question 3

explain that where there are energy transfers in a closed system there is no net change to the total energy in that system

Answer 3

– a closed system has a net change in energy of 0
- because law of conservation of energy

Question 4

what is a closed system

Answer 4

• a system treated completely on its own
• without any energy being exchanged to or from the surroundings
• net change in energy = 0

Question 5

Identify the different ways that the energy of a system can be changed

a) through work done by forces

Answer 5

1. a box is lifted up off the floor (making it a system)
2. work is done as the box is lifted against gravity
3. causing energy to be transferred to the box’s KINETIC and GPE stores

Question 6

Identify the different ways that the energy of a system can be
changed

b) in electrical equipment

Answer 6

1. electrical devices work by transferring energy between different energy stores

Question 7

Identify the different ways that the energy of a system can be
changed in electrical equipment ex electric toothbrush

Answer 7

(electric toothbrush is a system)
- it transferes energy electrically from chemical energy store of its battery to the kinetic energy store of its bristles
- some energy is transferred out of system by sound and heating

Question 8

Identify the different ways that the energy of a system can be
changed in electrical equipment ex hair dryer

Answer 8

(hair dryer is a system)
- transfers energy into system electrically from mains supply to kinetic energy store of fan inside it
- transfers energy electrically to the thermal energy store of the heating element and some is transferred away by sound

Question 9

Identify the different ways that the energy of a system can be
changed

c) in heating (when system is the pan of water

Answer 9

1. pan of water heated on a gas camping stove
2. when system is the pan of water => energy is transferred into system by ehating to the thermal enegry stores of the pan and the water (increasing their temperature)

Question 10

Identify the different ways that the energy of a system can be
changed

c) in heating (when system is the camping stove and the pan)

Answer 10

1. energy is transferred from the chemical energy store of the gas
2. to the thermal energy stores of the pan and water (increasing their temperature)

Question 11

describe how to measure the work done by a force

Answer 11

E = F * d

one joule of work is done when a force of one newton causes an object to move a distance of one metre

Question 12

what is energy equal to

Answer 12

work done

Question 13

what is the equation to work out how much work has been done

Answer 13

work done (E, J) = force (F, N) * distance moved in the direction of the force (m)

Question 14

what happens when a force moves an object through a distance

Answer 14

work is done on the object and energy is transferred

Question 15

Describe and calculate the changes in energy involved when a system is changed by work done by forces

Answer 15

• a force doing work can cause a change
  ex it often causes a rise in temperature, energy dissipated to, thermal energy stores of moving object, surroundings
• this means that the process is wasteful and the efficiency of the process is reduced
• efficiency equation

Question 16

Recall and use the equation to calculate the change in
gravitational PE when an object is raised above the ground

Answer 16

change in GPE = m * g * change in height

Question 17

Recall and use the equation to calculate the amounts of energy
associated with a moving object:

Answer 17

kinetic energy = 0.5 * m * (v squared)