Topic 3 - Conservation Of energy

Question 1

What is the equation for gravitational potential energy?

Answer 1

Mgh
Mass x Gfs x height
Kg x N/KG x M

Question 2

Equation of Kinetic energy

Answer 2

1/2 mv^2

Kg x m/s

Question 3

What is meant by the conservation of energy?

Answer 3

The 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 4

Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position. Ignore air resistance

Answer 4

Upwards: KE is converted to GPE
Peak: Maximum GPE zero KE
Downwards: GPE is converted to KE

Question 5

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

Answer 5

The total energy of the system remains constant due to the conservation of energy.

Question 6

Describe the energy changes that occur in a filament light-bulb

Answer 6

P,d is supplied energy is transferred by electricity which is then transferred into light (useful) and also thermal energy to the surroundings.

Question 7

Describe the energy transfers for a bungee jumper.

Answer 7

When falling, the gpe is converted to KE of the jumper.
As the cord tightens, KE is converted and stored as EPE.
At lowest point, the jumper’s initial GPE equals the EPE stored in the cord.

Question 8

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

Answer 8

Kinetic energy decreases since it is converted to elastic potential energy.
Since KE is proportional to (velocity)^2 as KE decreases, so does velocity.

Question 9

State two equations to calculate efficiency

Answer 9

Useful output energy/total input energy

Useful power output/total power output

Question 10

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

Answer 10

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

Question 11

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

Answer 11

Lower, meaning less energy transfer through them.

Question 12

State three methods of reducing heat loss in a building.

Answer 12

Double glazing
Loft and wall insulation
Thicker walls

Question 13

How can you reduce unwanted energy transfer in a mechanical system?

Answer 13

Reduce friction by lubricating moving parts

Question 14

How can the efficiency of a system be increased?

Answer 14

Reducing waste output (by lubrication, thermal insulation)

Recycling waste output (recycling thermal waste energy as input energy)