Energy changes in a system

What is a system

An object or group of objects

When a system is changed what also changes give example as well 

The way energy is store also changes 

For example when Ball is rolling and hitting the wall 

• The system is moving ball

• When it hits the wall some of the kinetic energy is transferred as sound 

What is the equation for kinetic energy?

½ x Mass x (Velocity)²

What is the equation for elastic potential energy?

½ x Spring Constant x (Extension)²

What is the equation for gravity potential energy?

Mass x Gravitational Field Strength x Height

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

define 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

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

●  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