Topic 3 - Energy

Question 1

What is meant by the conservation of energy?

Answer 1

• Total amount of energy in a closed system remains constant.
• Energy cannot be made or destroyed but can change from one form to another.

Question 2

Ignoring air resistance, describe the energy changes involved when a ball is thrown upwards and then returns to its starting position:

Answer 2

• Upwards: KE > GPE
• Peak: Maximum GPE, Zero KE
• Downwards: GPE > KE

Question 3

State any changes in the total energy of a ball that is kicked, assuming no external forces act.

Answer 3

Remains constant due to the conservation of energy.

Question 4

Describe the energy changes occurring in a filament-light bulb.

Answer 4

• Electrical energy transferred into light and thermal energy
• Light is a useful energy form, heat is waste energy.

Question 5

Describe the energy transfers for a bungee jumper

Answer 5

• When falling, the GPE is converted to KE of jumper
• As the cord tightens, KE is converted and stored as Elastic Potential Energy
• At lowest point, the jumpers initial GPE equals the EPE stored in the cord.

Question 6

Explain why a bungee jumper slows down once the cord begins to stretch.

Answer 6

• KE decreases as it’s converted to elastic potential energy.
• Since KE is proportional to v^2, as KE decreases, so does velocity.

Question 7

What is waste energy?

Answer 7

Energy that is not used by the device for:
- Its desired purpose
- Or not converted into the desired form.

Question 8

State the consequence for energy transfers of a material with a high thermal conductivity

Answer 8

• The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity.

Question 9

Do double-glazed windows have higher or lower thermal conductivity than single-glazed windows?

Answer 9

Lower, meaning less energy transfers through them