P1 Energy

Question 1

What is the equation for kinetic energy?
Give units for all quantities involved.

Answer 1

½ m v^2
½ x Mass x (Velocity)^2
Energy (J), Mass(kg), Velocity(m/s)

Question 2

What is the equation for elastic potential energy ? Give units for all quantities involved

Answer 2

½ k x^2
½ x Spring Constant x (Extension)^2
Energy (J), Spring Constant (N/m), Extension(m)

Question 3

What is the equation for gravity potential energy ? Give units for all quantities imvolved.

Answer 3

mgh
Mass x Gravitational Field Strength × Height
Energy (J), Mass(kg), Gravitational Field Strength (N/kg),
Height (m)

Question 4

Define the ‘Specific Heat Capacity’ of a substance.

Answer 4

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

Question 5

State the units for specific heat capacity

Answer 5

J/°C/kg
Joules/Degree Celsius/Kilogram

Question 6

What is the definition of ‘Power’ ?

Answer 6

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

Question 7

State two equations for power . Give units for all quantities involved

Answer 7

power = energy transferred/time
power = work done/time
Energy (J), Work Done (J), Time (s)

Question 8

What is the unit of power?

Answer 8

Watt (W)

Question 9

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 9

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

Question 10

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

Answer 10

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

Question 11

Describe the energy transfers for a bungee jumper

Answer 11

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

Question 12

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

Answer 12

• 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 13

Give examples of chemical energy stores.

Answer 13

• Food
• Fuel (eg. Wood , coal , petrol)
• Batteries

Question 14

State 4 different stores of energy.

Answer 14

1. Kinetic energy
2. Gravitational Potential Energy
3. Elastic Potential Energy
4. Chemical Energy