Conservation of energy (3)

Question 1

What is the equation to find change in gravitational potential energy?

Answer 1

GPE = m x g x h
GPE - gravitational potential energy (J)
m - mass (kg)
g - gravitational field strength (N/kg)
h - change in height (m)

Question 2

What is the equation to find kinetic energy?

Answer 2

KE = 1/2 x m x v^

KE = kinetic energy (J)
m = mass (kg)
v = velocity (m/s)

Question 3

What is meant by the conservation of energy?

Answer 3

Energy can be stored, transferred between stores and dissipated but can never be created or destroyed. The total energy in a closed system has no net change.

Question 4

How can energy be transferred?

Answer 4

Mechanically - a force acting on an object.
Electrically - a charge doing work.
By heating - energy transferred from a hotter to a colder object.
By radiation - energy transferred by waves.

Question 5

How do mechanical processes become wasteful?

Answer 5

When there are mechanical transfers going on, friction forces have to be overcome. The energy needed to overcome these forces is transferred to thermal energy stores and is quickly dissipated.

Question 6

What are ways of reducing unwanted energy transfers?

Answer 6

Lubrication:
To reduce the amount of frictional forces needed to be overcome in a mechanical energy transfer lubricants are used.
Insulation:
When an object is heated, particles in it start to vibrate and collide with each other transferring kinetic energy stores to each other. This is called conduction. Gasses have a low thermal conductivity. Some houses have cavity walls to reduce the amount of thermal conduction so less thermal energy is transferred outside.

Question 7

What is the equation for efficiency?

Answer 7

Efficiency = (useful energy transferred by the device)/(total energy supplied to the device)