Topic 8 – Energy: Forces Doing Work-Power Flashcards
What is the definition of ‘Power’?
The rate at which energy is transferred (or rate at which work is done).
State two equations for power. Give SI units for all quantities involved.

power = energy transferred / time power = work done / time
What is the unit of power?
Watt (W)
What is one Watt equivalent to
1 Joule per second (J/s).
what does a power rating of 10W mean for an electrical device?

it converts 10 Joules of energy every second.
Two motors lift the same mass through the same height. Motor A does this in half the time of Motor B. Which dissipates the most power?
Motor A.
The energy transferred is the same but the time taken is less (P=E/t)
what is efficiency?
The proportion of energy that is converted usefully, rather than wasted/dissipated.
How do you calculate efficiency?
efficiency = useful energy out / total energy in
What are the units of efficiency
Efficiency is a ratio so has no units, but it can be expressed as a percentage.
