Conservation of Energy and Power Flashcards
Energy (12 cards)
What does the conservation of energy principle state?
Energy is always conserved.
Energy can be transferred, stored, or dissipated, but never created or destroyed.
What happens to energy during transfers?
Not all energy is transferred usefully; some is always dissipated.
Dissipated energy is often referred to as wasted energy.
What is dissipated energy sometimes called?
‘Wasted energy’.
This occurs when energy is stored in a way that is not useful, typically as thermal energy.
In the context of a mobile phone, where does useful energy transfer occur?
From the chemical energy store of the battery.
Some energy is dissipated as thermal energy, making the phone warm during use.
Describe the energy transfer in a closed system involving a cold spoon and hot soup.
Energy is transferred from the thermal energy store of the soup to the thermal energy store of the spoon.
The net change in energy is zero, as no energy leaves the closed system.
What is power defined as?
The rate of doing work or energy transfer.
It is how much energy is transferred per second.
What unit is power measured in?
Watts.
One watt equals one joule of energy transferred per second.
How can power be calculated?
Using the equations: P = E/t and P = W/t.
Where P is power, E is energy transferred, W is work done, and t is time.
True or False: A powerful machine is defined by the strength of force it can exert.
False.
A powerful machine transfers a lot of energy in a short amount of time.
In a race between two identical cars, what determines which car is more powerful?
The car with the more powerful engine will reach the finish line faster.
Both cars transfer the same amount of energy, but over different times.
If Motor A lifts 8000 J of work in 50 s, what is its power?
160 W.
Power is calculated using P = W/t, where P = 8000 J / 50 s.
How long does Motor B take to lift the same weight as Motor A?
300 s.
Motor B is less powerful than Motor A despite transferring the same amount of energy.
