4.15 use the relationship between power, work done (energy transferred) and time taken:

Power = work done / time taken

P = W / t

For example...

A motor transfers 4.8kJ of useful energy in 2 minutes. Find it's power output...

As work done is the same as energy transferred, we know that 4.8kJ of work was done. Therefore...

4800 / (2 x 60) = 4.8 / 120 = 40 W

NOTE: remember to convert kJ to J and minutes into seconds.

4.14 describe power as the rate of transfer of energy or the rate of doing work

Power is the rate of energy transfer, or the rate of doing work, it is different to force and energy. The unit for power is watts (W), 1 watt = 1 joule of energy transferred per second. This means a watt is the same as a 'joule per second', they are interchangeable, watt is more commonly used just because few people may get confused with 'joule' and 'joule per second' (which are vert different things).

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

When something is falling, GPE is being converted into KE. This means that the further it goes, the faster it falls (well, until it reaches terminal velocity), as it is gaining more KE the further it has fallen. This equation may be useful to remember...

Kinetic energy gained = gravitational potential energy lost

4.12 know and use the relationship: kinetic energy = 1/2 x mass x speed2

0. 0. kinetic energy = 0.5 × mass × speed2 
      
   
   
   KE = 0.5 x m x v 2 
   

4.11 know and use the relationship: gravitational potential energy = mass x g x height

Gravitational energy = mass x g x height

GPE = m x g x h

NOTE: g stands for gravitational constant, which is around 9.8 on earth (rounded to 10 for exam purposes)

4.10 understand that work done is equal to energy transferred

Pretty self explanatory... work done is another way of saying energy transferred.

Basically, when a force is moves on an object, energy is transferred and work is done.

4.9 know and use the relationship between work, force and distance moved in the direction of the force:

Work done = force x distance moved


W = F x d


Example...

A tow truck drags a car 5m with a force of 340N, find the work done.

5 x 340 = 1700J

NOTE: Work done is measured in Joules, this is because it is the same as energy transferred (and energy is measured in Joules)