Measuring Energy (Work) & Power: Activity

Activity (Energy [as Work], Ew = F x d)

Work (J) (energy) is measured in units called joules. Work (joules) = force (newtons) x distance (metres).
  1. Calculate the work done when a 20 (newton) force moves an object 10m (metres).
  2. Calculate the work done when a 200N force moves an object 1m.
  3. Calculate the work done when a 25N force moves an object 100m.
  4. A person whose weight is 500N climbs up stairs 3m. How much work is done? How much energy is required?
  5. A book weighs 10N and is lifted 2m. How much work is done in lifting the book?

Activity (Power, P = E/t)

Power is the rate at which energy is transferred or the rate at which work is done. Work is measured in watts (W), where a watt is one joule per second.
  1. In order to do 20J (joules) of work in two seconds, what is the power required?
  2. In order to do 200J of work in two seconds, what is the power required?
  3. In order to do 2000J of work in two seconds, what is the power required?
  4. How much power would be required for a person whose weight is 500N to run up a flight of stairs 3m high in 4 seconds?
  5. Your weight (in newtons) is equal to your mass (in kilograms) times 9.8. How much power would you need to run up a 3m high flight of stairs in 4 seconds?

Activity (Purchasing Electrical Energy, E = P x t)

Electrical energy is purchased by the kilowatt-hour rather than the joule. The price varies from a few cents per kilowatt-hour to several dollars per kilowatt hour, depending upon the production and delivery mechanisms of the electrical energy.

1 kilowatt-hour = 3.6 million joules (1kWh =3.6MJ)

To calculate the energy E consumed (in kilowatt-hours) we use E = P x t (where the power P is in watts multiplied by the time t in hours).

  1. How much energy (in kWh) is used by a 100W(watt) bulb burning for 10 hours continuously?
  2. How much energy (in kWh) is used by a 1500W(watt) electrical heater which operates 10 hours each day?
  3. How much energy (in kWh) is used by a 1100W(watt) hair dryer used for 10 minutes each day for the month of April?
  4. An electric car motor is run with a power output of 30kW for 3 hours. How much energy is used?
  5. An electric car motor is run with a power output of 90kW for 20 minutes. How much energy is used?

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