6.1.2 Conservation and Dissipation of Energy

Question 1

How can we reduce the amount of energy lost due as waste energy due to friction?

Answer 1

Lubricate the system with oil.

Question 2

How can we reduce the amount of energy lost due as waste energy due to thermal losses?

Answer 2

Insulate the system with a thermal insulator (i.e. fibre glass wool etc.)

Question 3

What is the equation relating efficiency and energy?

Answer 3

Efficiency = useful energy out / total energy in x 100 %

Question 4

What is the equation relating efficiency and power?

Answer 4

Efficiency = useful power out / total power in x 100 %

Question 5

What is efficiency?

Answer 5

It is a measure of how much energy put into a system comes out as useful energy.

Question 6

Why is efficiency important?

Answer 6

Increasing the efficiency of system means that less energy is required to do a task;
this is more cost effective;
and uses fewer (natural) resources.

Question 7

What is the equation relating power, work done and time?

Answer 7

Power = work done / time
P = W.d./ t

Question 8

What is the unit of power?

Answer 8

Watts (W)

Question 9

What is time measured in?

Answer 9

Seconds (s)

Question 10

If time is given in days what should you do?

Answer 10

Convert the time into seconds

Question 11

What are the conversions for time in:
minutes,
hours,
days,
years?

Answer 11

minutes = x 60
hours = x 60 x 60
days = x 60 x 60 x 24
years = x 60 x 60 x 24 x 365.25

Question 12

How do we define a Watt?

Answer 12

It is the power when 1 joule is transferred in 1 second.

Question 13

Motor A and motor B lift a 100 g mass the same height. Motor A does it quicker than motor B. What can you say about the two motors?

Answer 13

Motor A is more powerful than motor B.