Energy changes in a system 1.1

Question 1

Define the ‘Specific heat capacity’ of a substance

Answer 1

The amount of energy needed to raise the temperature of 1 kilogram of a substance by 1 degree celcius

Question 2

State the units for Specific Heat Capacity

Answer 2

J/°C/kg

Joules/Degree Celsius/Kilogram

Question 2

State the units for Specific Heat Capacity

Answer 2

J/°C/kg

Joules/Degree Celsius/Kilogram

Question 3

What is the definition of ‘Power’?

Answer 3

The rate at which energy is transferred (or rate at which work is done)

Question 4

What is the unit of power?

Answer 4

Watt (W)

Question 5

Two motors lift the same mass through the same height. Motor A does this in half the time of Motor B. Which dissipates the most power?

Answer 5

Motor A.

The energy transferred is the same but the time taken is less (P=E/t)

Question 6

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

Answer 6

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

Question 7

Describe the energy transfers for a bungee jumper

Answer 7

• When falling, the GPE is converted to KE of jumper
• As the cord tightens, KE is converted and stored as EPE
• At lowest point, the jumpers 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 EPE

- Since KE is proportional to velocity², as KE decreases, so does velocity

Question 9

Give examples of chemical energy stores

Answer 9

• Food
• Fuel (e.g. wood, coal, petrol)
• Batteries

Question 10

State 4 different stores of energy

Answer 10

• Kinetic energy
• Gravitational potential energy
• Elastic potential energy
• Chemical energy