Power and work done

• How many different definitions of power are there?

  Two
• What does the first definition of power state?

  Power is the rate at which energy is transferred.
• What is the equation for power based on energy transfer?

  $Power =$$\frac{\text{Energy Transferred}}{\text{Time}}$
• How does work done relate to energy transferred?

  Work done is a special measure of the energy transferred when a force moves an object over a certain distance.
• In what unit is energy transferred and work done measured?

  Joules
• In what unit is power measured?

  Watts
• In what unit is time measured in power calculations?

  Seconds
• How do you calculate power using energy transferred?

  • Power is calculated by dividing the energy transferred by the time it took to transfer that energy
  • Equation: $Power =$$\frac{\text{Energy Transferred}}{\text{Time}}$
• What is the second definition of power?

  • Power is the rate at which work is done.
  • Equation: $Power =$$\frac{\text{Work Done}}{\text{Time}}$
• What condition distinguishes work done from energy transferred in power equations?

  Work done involves a force moving an object over a distance.
• A lamp transfers 1200 joules over 20 seconds. What is its power?

  60 Watts
• If Lamp 1 has a power of 60 watts and Lamp 2 has a power of 50 watts, which lamp is more powerful?

  Lamp 1
• How much energy is transferred by an 1100-watt microwave that runs for 180 seconds?

  198000 Joules
• How do you convert Joules to Kilojoules?

  Divide Joules by 1000.
• Convert 198000 Joules to Kilojoules.

  198 Kilojoules
• To push a car down the street, you do 9000 Joules of work over 20 seconds. What is the power you are using?

  450 Watts