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Power for grade 8

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  • A computer uses 7200 J of energy in 120 s. What is its power?
    60 W
  • A bicycle dynamo transfers kinetic energy into another form to power the light. What is that form?
    Electrical
  • A motor transfers 1200 J of energy in 60 s. What is its power?
    20 W
  • A toaster transfers 500 J of electrical energy into 400 J of heat and 100 J of light. What is the main useful energy form?
    Heat
  • A light bulb receives 100 J of electrical energy but only 20 J becomes light. Calculate its efficiency.
    20%
  • A fan uses 80 W for 15 minutes. Energy transferred?
    72,000 J
  • A person uses chemical energy from food to run. What is the useful energy transfer?
    Kinetic
  • A washing machine operates at 500 W for 1.5 h. Energy used in joules?
    2,700,000 J
  • In a hairdryer, electrical energy is transferred into useful energy types. Name two useful energy forms.
    Kinetic and heat
  • An 8 kW shower runs for 10 min. Energy used in joules?
    4,800,000 J
  • A solar panel transfers light energy into another form. What is it?
    Electrical
  • A loudspeaker uses 100 J of electrical energy in 2 s but only produces 60 J of sound. What is its power output in sound?
    30 W
  • In a speaker, electrical energy is transferred mainly into one useful form. What is it?
    Sound
  • A TV consumes 300 J in 5 s. Calculate its power.
    60 W
  • A television transfers electrical energy into light and sound. Name one wasted energy type.
    Heat
  • A loudspeaker transfers 60 J of electrical energy into 48 J of sound energy. Calculate its efficiency.
    80%
  • Convert 1 kWh to joules.
    3,600,000 J
  • A lamp transfers 200 J of energy in 10 s. What is its power?
    20 W
  • A phone charger transfers 180 J of energy in 6 s. What is its power?
    30 W
  • A motor transfers 500 J of electrical energy and produces 400 J of kinetic energy. How much energy is wasted?
    100 J
  • A kettle is rated at 2000 W. Energy used in 30 s?
    60,000 J
  • A candle flame transfers chemical energy mainly into two useful forms. What are they?
    Light and heat
  • A lift motor transfers 72,000 J in 40 s. Power?
    1,800 W
  • A TV transfers 3000 J of energy in 50 s. What is its power?
    60 W
  • A torch transfers chemical energy in the battery into electrical energy, which then becomes light energy. Name one wasted energy form.
    Heat
  • A kettle transfers 200 J of electrical energy to 160 J of heat energy in the water. What is its efficiency?
    80%
  • A bulb uses 60 J of electrical energy every second. What is its power?
    60 W
  • A wind turbine transfers kinetic energy from the wind into another form. What is it?
    Electrical
  • Convert 2 kWh to joules.
    7,200,000 J
  • A kettle uses 2000 W of power for 20 s. How much energy does it transfer?
    40,000 J
  • A motor transfers 600 J in 3 minutes. Calculate its power.
    3.3 W
  • A kettle uses 5000 J of energy in 25 s. What is its power?
    200 W
  • A heater transfers 600 J of energy in 30 s. What is its power?
    20 W
  • A light bulb transfers 120 J in 2 s. What is its power?
    60 W
  • A motor takes in 400 J of electrical energy and delivers 300 J of kinetic energy in 10 s. What is its power output?
    30 W
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