Power and Work DoneAQA GCSE Physics: Flashcards

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When is work done on an object?

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When is work done on an object?: Whenever a force moves it through a distance, or a current flows through a component.
State the equation linking power, energy and time.: P = E/t
State the equation linking power, work done and time.: P = W/t
What is the unit of power?: The watt (W), equal to one joule per second.
Two motors lift the same load to the same height. Motor A takes 2 s, Motor B takes 8 s. Which has the greater power?: Motor A - same work done in less time means greater power.
A machine does 1000 J of work in 5 s. Calculate its power.: P = 1000/5 = 200 W
If a motor has a power of 50 W, how much energy does it transfer in 10 s?: E = P × t = 50 × 10 = 500 J
Why can two systems transfer the same amount of energy but have different powers?: Because they take different amounts of time to transfer that energy.
How is gravitational potential energy related to work done against gravity when lifting an object?: The work done lifting the object equals the gravitational potential energy gained, Ep = mgh.
How is kinetic energy related to work done accelerating an object?: The work done accelerating the object from rest equals the kinetic energy gained, Ek = ½mv².
A crane lifts a load doing 4000 J of work in 8 s. Find its power.: P = 4000/8 = 500 W