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Work done and power

We can link the concept of work done to power!

Power usually refers to energy, as we’ll revisit in a minute, but since work done just means energy transferred, we can also link power to work done.

The normal formula for power is:

Or, in symbols:

Where:

  • is the power, in watts,
  • is the energy transferred, in joules,
  • is the time taken, in seconds,

Using the knowledge that work done is just the same thing as energy transferred, we can write this as:

Or in symbols:

Where:

  • is the power, in watts,
  • is the work done, in joules,
  • is the time taken, in seconds,

A machine does 500 J of work in 10 s. What is the power of the machine?

Section titled “A machine does 500 J of work in 10 s. What is the power of the machine?”

A machine does 1000 J of work in 20 s. What is the power of the machine?

Section titled “A machine does 1000 J of work in 20 s. What is the power of the machine?”

A machine has a power of 200 W and does 400 J of work. How long does it take to do the work?

Section titled “A machine has a power of 200 W and does 400 J of work. How long does it take to do the work?”

A machine has a power of 150 W and does 300 J of work. How long does it take to do the work?

Section titled “A machine has a power of 150 W and does 300 J of work. How long does it take to do the work?”

A mechanical device does 50 W of power over a period of 5 s. How much work does it do?

Section titled “A mechanical device does 50 W of power over a period of 5 s. How much work does it do?”

A mechanical device does 75 W of power over a period of 8 s. How much work does it do?

Section titled “A mechanical device does 75 W of power over a period of 8 s. How much work does it do?”