Work, Power and Efficiency - Topic 1

Question 1

What is it meant by the term “work”

Work, Power and Efficiency

Answer 1

Work is the amount of energy shifted.

Question 2

What is meant by mechanical work?

Work, Power and Efficiency

Answer 2

The energy shifted by a force

Question 3

What are the units of work?

Work, Power and Efficiency

Answer 3

Joules, J

Question 4

What is the equation for calculating mechanical work?

Work, Power and Efficiency

Answer 4

Work done = Force * distance
W = F * d

Question 5

What force do you do work against when you lift an object onto a shelf?

Work, Power and Efficiency

Answer 5

Gravity

Question 6

What force do you do work against when you push an object across a rough surface?

Work, Power and Efficiency

Answer 6

Friction

Question 7

What force do you do work against when you push the opposite poles of two magnets together?

Work, Power and Efficiency

Answer 7

Magnetic force between the magnets

Question 8

What is meant by the term power?

Work, Power and Efficiency

Answer 8

It is the rate of energy transfer (or the rate of work done).
This is the energy transferred (or work done) per second.

Question 9

What are the units of power?

Work, Power and Efficiency

Answer 9

Watts, W

Question 10

What is the equation for calculating power?

Work, Power and Efficiency

Answer 10

Power = Energy transferred/Time taken

Question 11

One watt is the same as…

Work, Power and Efficiency

Answer 11

1 Joule per second.

Question 12

What is meant by the term efficiency?

Work, Power and Efficiency

Answer 12

It is the fraction of the total energy that is useful.

Question 13

What is the equation for efficiency, in terms of energy?

Work, Power and Efficiency

Answer 13

Efficiency = Useful energy/Total energy

Question 14

What is the equation for efficiency, in terms of power?

Work, Power and Efficiency

Answer 14

Efficiency = Useful power/Total power

Question 15

What are the units of efficiency?

Work, Power and Efficiency

Answer 15

Efficiency has no units, because it is a ratio.
Efficiencies are written as a decimal or a percentage.

Question 16

What is the smallest value of efficiency?

Work, Power and Efficiency

Answer 16

0

Question 17

What is the largest possible value of efficiency?

Work, Power and Efficiency

Answer 17

1

Question 18

Explain why in practice it is impossible to have an efficiency of 1 for an energy transfer.

Work, Power and Efficiency

Answer 18

Because some energy is dissipated to other non-useful stores

Question 19

State and explain how energy dissipation can be reduced for objects moving through air or water.

Work, Power and Efficiency

Answer 19

Make them more streamlined, to reduce the amount of drag/air resistance on the object

Question 20

State and explain how energy dissipation can be reduced for surfaces moving against each other.

Work, Power and Efficiency

Answer 20

Lubricate the surfaces with oil, to reduce the amount of friction

Question 21

State and explain how energy dissipation can be reduced for a house.

Work, Power and Efficiency

Answer 21

· Loft insulation
· Cavity wall insulation
· Double glazing
· Use materials with low thermal conductivity

Question 22

Give an example of a material with a high thermal conductivity.

Work, Power and Efficiency

Answer 22

Metal