10.3 Power Flashcards
How can energy be transferred from one object to another
Work done - by a force due to one object making the other object move
Heat transfer - from a hot object to a cold object. Heat transfer can be due to conduction or convection or radiation
Electromagnetic radiation, electricity and sound waves
The more energy transferred per second, the greater the ______ of the transfer process
Power
What is power defined as
The rate of transfer of energy
What is the unit of power
Watt
What is awatt equal to
An energy transfer of 1 joule per second
One kW=1000W
If energy ΔE is transferred steadily in time Δt
Power P=ΔE/Vt
Where energy is transferred by a force doing work, the energy transferred is equal to the work done, thus…
Power P=ΔW/Δt
How to calculate your muscle power
Gain of potential energy=weight*total height gain
Muscle power=energy transferred/time taken=weight*height gain/time taken
When a powered object moves at constant velocity at constant height…
…the resistive forces (eg. friction, air resistance, drag) are equal and opposite to the motive force
Work done by the engine is transferred into the internal energy of the surroundings by the resistive forces
For a powered vehicle driven by a constant force F moving at speed v:
The work done per second=force*distance moved per second
SO…
Output power P=Fv
When a powered object gains speed, the ______ force exceeds the ______ forces on it
Output
Resistive
As the resistive forces of a vehicle speeding up increase the internal energy of the surroundings:
The motive power=energy per second wasted due to the resistive force + the gain of kinnetic energy per second
What weight must a truck with six or more axles on UK roads not exceed
44 tonnes
44 tonnes to kg
44000kg
Why is there a limit to the weight of trucks with six or more axles
To prevent damage to roads and bridges
