physics aqa gcse energy changes in a system 4.1.1

What is the equation for kinetic energy?

½ m v²

½ x Mass x (Velocity)²

Energy (J), Mass(kg), Velocity(m/s)

What is the equation for elastic potential energy?

½ kX²

½ x Spring Constant x (Extension)²

Energy (J), Spring Constant (N/m), Extension(m)

What is the equation for gravity potential energy?

mgh

Mass x Gravitational Field Strength x Height

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

Define the ‘Specific Heat Capacity’ of a substance.

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

State the units for Specific Heat Capacity.

J/°C/kg

Joules/Degree Celsius/Kilogram

What is the definition of ‘Power’?

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

State two equations for power. 

power = energy transferred/time

power = work done/time

Energy (J), Work Done (J), Time (s)

What is the unit of power?

Watt (W)

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?

Motor A.

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

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

● Upwards: KE is converted to GPE

● Peak: Maximum GPE, zero KE

● Downwards: GPE is converted to KE

Describe the energy transfers for a bungee jumper.

● 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

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

● Kinetic energy decreases since it is converted to elastic potential energy

● Since KE is proportional to (velocity)², as KE decreases, so does velocity.

Give examples of chemical energy stores.

● Food

● Fuel (eg. wood, coal, petrol)

● Batteries

State 4 different stores of energy.

1. Kinetic Energy

2. Gravitational Potential Energy

3. Elastic Potential Energy

4. Chemical Energy

5. Nuclear Energy

6. Thermal Energy

7. Magnetic Energy

8. Electrostatic Energy