Work And Power

Question 1

How energy is transferred mechanically

Answer 1

To transfer energy mechanically, you have to use a force and move something a distance. We then say that the force is ‘doing work’

In these examples, a force is causing energy to be transferred mechanically:

E.g. Drawing a bow
Where/what is the force that is ‘doing work’ - her arm pulling the string
Energy transferred from - Chemical (food) —> Kinetic
Energy transferred to - Elastic potential

E.g.Dragging a suitcase at a steady speed
Where/what is the force that is ‘doing work’ - the person pulling the suitcase
Energy transferred from - chemical
Energy transferred to - thermal in the wheels (wasted)

You may think that the energy transferred to is kinetic. However, it says steady speed which therefore means there is no kinetic energy

Question 2

The formula for calculating work done

Answer 2

Work done in any mechanical transfer - Force used x distance moved

W = F x d

Question 3

Triangle for calculating work done

Answer 3

Work done at the top, force in the left and distance on the right

Question 4

Units for formula for work done

Answer 4

Work done - Joules
Force - Newtons
Distance - metres

Question 5

Definition of power

Answer 5

The rate at which energy is transferred

Question 6

Formula to work out power (normal formula and for mechanical energy transfer)
Units

Answer 6

Power = energy transferred / time taken

Power is measured in Watts (W)
The energy must be in Joules
And the time has to be in seconds

But because we are working with mechanical energy transfer it will become:
Power = Work done / time taken

Question 7

Formula for change in gravitational potential energy

If an items drops in height, what will happen?
If an item gains in height, what will happen?
If an item falls over, what will happen?

Answer 7

Change in gravitational potential energy = mass x gravitational field strength x height change

GPE - m x g x h

If an item drops in height, it loses GPE
If an item gains in height, it gains GPE
If an object falls over, it loses GPE because its centre of gravity drops in height

Question 8

Triangle for power - with work done

Answer 8

Work done at the top, power left, time right

Question 9

Kinetic energy formula

Answer 9

Energy in kinetic energy store (J) = ½ x mass (m) x (speed)^2

Question 10

Triangle for kinetic energy

Answer 10

Kinetic energy at the top, 1/2 in the left, mass in the middle, speed squared on the right