CONSERVATION OF ENERGY

Question 1

the principle of conservation of energy

Answer 1

energy cannot be created or destroyed

Question 2

energy can be transferred

Answer 2

usefully, stored or dissipated

Question 3

when energy is transferred is it all useful energy?

Answer 3

not all of the energy transferred is useful some of it is dissipated during energy transfer

Question 4

what is dissipated energy?

Answer 4

waste energy (spreading out)

Question 5

describe the energy transfer in a phone?

Answer 5

a phone - system

• energy is usefully transferred from the chemical energy store of the battery in the phone
• some is dissipated to the thermal energy of the phone

Question 6

give an example of energy transfer in a closed system (cold spoon dropped into an insulated flask of hot soup, then sealed)

Answer 6

flask - thermal insulator
spoon and soup - closed system
energy is transferred from the thermal energy of the soup to the useless thermal energy of the spoon

Question 7

what is power?

Answer 7

the rate of energy transfer

Question 8

one watt =

Answer 8

1 joule of energy transferred per second

Question 9

P = W/t

Answer 9

power (W) = work done (J) / time (s)

Question 10

define a power machine?

Answer 10

transfers a lot of energy in a short space of time

Question 11

explain what happens when a pendulum is in motion

Answer 11

• as it swings down and towards the centre its GPE store decreases its kinetic energy store increases
• as it moves upwards its GPE store increases as its kinetic energy store decreases

Question 12

what would happen to the pendulum in a closed system? (vacuum)

Answer 12

in a vacuum it would swing forever as there’s no air resistance acting on it so no energy would be transferred

Question 13

what happens when the rope is slack during bungee jumping?

Answer 13

the energy is transferred from the GPE store to the kinetic energy store as the person accelerate towards the ground due to the force of gravity

Question 14

what happens when the rope tightens during bungee jumping?

Answer 14

their fall slows down as the force of the rope reduces —the speed of their kinetic energy store decreases and their elastic potential energy store increases as the rope stretches
-as they begin to stop and all of the energy from their kinetic energy store is transferred to elastic potential energy store of the rope

Question 15

what happens at the bottom of the bungee jump?

Answer 15

the rope recoils and pulls them back

• they rise and energy in the elastic potential energy store of the rope decreases
• their kinetic energy store increases until the rope becomes slack

Question 16

what happens at the top of the bungee jump?

Answer 16

their kinetic energy store decreases to 0 and their GPE store increases as they ascend
-they don’t return to the og height because some energy was transferred to the thermal energy store of the surroundings by heating as the rope stretched and then shortened again