P7

Question 1

What is the conservation of energy principle?

Answer 1

Energy is never created or destroyed, only transferred.

Question 2

What energy transfers happen when an object is thrown upwards?

Answer 2

• Kinetic energy → Gravitational potential energy (GPE)

• Then GPE → KE as it falls back down

Question 3

What happens when an object is projected up a slope?

Answer 3

• KE is transferred to GPE going up

• GPE is transferred back to KE going down

Question 4

What energy transfer occurs when a moving object hits a wall?

Answer 4

• KE → Elastic potential energy (EPE) when it squashes

Question 5

What happens when an object is accelerated by a constant force?

Answer 5

The force does work, transferring energy to KE in the object

Question 6

What happens when a vehicle slows down?

Answer 6

KE → Thermal energy due to friction between brakes, wheels, and road

Question 7

What energy transfer happens when a kettle boils water?

Answer 7

Electrical energy → Thermal energy in the water

Question 8

Q: What happens to particles when heat is transferred to an object?

Answer 8

They gain kinetic energy, increasing the temperature.

Question 9

What must energy overcome during heating?

Answer 9

The object’s specific heat capacity.

Question 10

What does work done mean in physics?

Answer 10

Energy transferred when a force moves an object.

Question 11

Does the force give energy to the object?

Answer 11

No — but applying force over a distance requires energy (i.e., does work).

Question 12

What happens when current flows through a resistor?

Answer 12

Work is done against resistance, transferring KE to heat.

Question 13

What is the formula for work done?

Answer 13

W = F x d

(Work = Force × Distance)

Question 14

What is the equation for energy using power and time?

Answer 14

E = P x t

Question 15

What is the formula for kinetic energy?

Answer 15

KE = 1/2 mv^2

Question 16

What is the formula for gravitational potential energy?

Answer 16

GPE = mgh

Question 17

What is the formula for elastic potential energy?

Answer 17

EPE = 1/2kx^2

Question 18

What happens to energy when it is lost?

Answer 18

It is dissipated into waste forms like heat, sound, or light.

Question 19

Give 3 examples of wasted energy:

Answer 19

1. Wires heating up
2. Sound when a ball hits a wall
3. Light sparks from friction

Question 20

What causes energy loss in electrical systems?

Answer 20

Heating of wires

• Motors heating up

• Inefficient contacts

Question 21

What is an appliance’s power rating?

Answer 21

A label showing how much power and voltage it uses.

Question 22

What does a higher power rating indicate?

Answer 22

More energy used per second, possibly lower efficiency.

Question 23

What is the formula for efficiency?

Answer 23

efficiency = useful energy output/total energy output

Question 24

What happens to power loss as current increases?

Answer 24

Power loss increases, due to

P = I^2R

Question 25

How can efficiency be increased?

Answer 25

• Recycle or capture waste energy • Lubricate moving parts to reduce friction • Add thermal insulation to stop heat loss

Question 26

How is heat lost from buildings?

Answer 26

Through walls, especially without insulation.

Question 27

What happens in uninsulated cavity walls?

Answer 27

Convection currents form and carry energy away.

Question 28

What does insulation do?

Answer 28

Prevents convection currents • Weakly conducts heat • Reduces rate of cooling

Question 29

What else reduces the rate of cooling?

Answer 29

Thicker walls.

Question 30

What does the conservation of energy mean in a system?

Answer 30

Even when energy is transferred, the total energy of a closed system stays the same — no net change.

Question 31

What is a kWh and how is it used?

Answer 31

1 kilowatt-hour (kWh) = energy transferred by a 1 kW appliance in 1 hour • Used to measure electrical energy use at home.

Question 32

How does energy transfer from mains or batteries in homes?

Answer 32

From batteries: DC current transfers energy • From mains (AC): energy flows into devices • Some energy is wasted as heat, especially in motors and heaters

Question 33

How do power ratings relate to energy transfer in appliances?

Answer 33

Higher power = more energy transferred per second, affecting how much energy is stored/used during operation.

Question 34

How does wall thickness affect building cooling rate?

Answer 34

Thicker walls reduce heat loss • Low thermal conductivity slows down cooling • Affects how fast buildings lose energy