P1 Conservation and dissipation of energy

Question 1

Name the five energy stores

Answer 1

kinetic, gravitational potential, elastic potential, thermal, chemical

Question 2

Name the four ways in which energy can be transferred.

Answer 2

heating, waves, electric current, mechanically (by forces)

Question 3

What is a system?

Answer 3

an object or group of objects

Question 4

What is a closed system?

Answer 4

a system where no energy can be transferred to or from the surroundings - the total energy in the system stays the same

Question 5

What is work done?

Answer 5

energy transferred when a force moves an object

Question 6

What is the unit for energy?

Answer 6

joules (J)

Question 7

What is one joule of work?

Answer 7

the work done when a force of 1 N causes an object to move 1 m in the direction of the force

Question 8

Describe the energy transfer when a moving car slows down.

Answer 8

energy is transferred mechanically from the kinetic store of the car to the thermal store of its brakes.
Some energy is dissipated to the thermal store of the surroundings

Question 9

Describe the energy transfer when an electric kettle is used to heat water.

Answer 9

the electric current in a kettle transfers energy to the heating element’s thermal store - energy is then transferred by heating from the heating element’s thermal store to the thermal store of the water

Question 10

Describe the energy transfer when a ball is fired using an elastic band.

Answer 10

energy is transferred mechanically from the elastic store of the elastic band to the kinetic store of the band - some energy is dissipated to the thermal store of the surroundings

Question 11

Describe the energy transfer when a battery powered toy car is used.

Answer 11

energy is transferred electrically from the chemical store of the battery to the kinetic store of the toy car - some energy is dissipated to the thermal store of the surroundings

Question 12

Describe the energy transfer when a falling apple hits the ground.

Answer 12

energy is transferred from the kinetic store of the apple and dissipated to the thermal store of the surroundings by sound waves

Question 13

Name the unit that represents one joule transferred per second.

Answer 13

watt (W)

Question 14

A motor is 30% efficient. What does that mean?

Answer 14

30% of the energy is usefully transferred and 70% is dissipated