Work done and power

• What is the relationship between work and forces in physics?

  Work is done with forces and energy
• When is work considered done in physics?

  When a force moves an object through distance
• What happens to energy when work is done on an object?

  Energy is transferred to the object
• What is required to make something move in terms of forces?

  • A force needs to act on it
  • The force acts as a source of energy
  • Examples include fuel or food
• How is energy transferred when a force moves an object?

  Energy is transferred mechanically from one store to another
• What is the unit of work done when a force of one newton moves an object one meter?

  One joule
• What does it mean if energy is transferred 'usefully'?

  It means energy is used for a purpose, like lifting
• How does wasted energy differ from useful energy in work done?

  Wasted energy does not perform useful work
• How much work is done when a force of one newton moves an object one meter?

  One joule
• How can you express the work done in lifting a weight?

  Work = force x distance
• If a force of $70 \text{ N}$ lifts an object $1.2 \text{ m}$, how much work is done?


  $84 \text{ J}$
• What happens to temperature when work is done on an object?

  Temperature often increases due to energy dissipation
• What does reduced efficiency in a process indicate?

  More energy is wasted rather than used effectively
• What is the formula for efficiency in energy transfer?

  Efficiency = useful energy transferred / total energy supplied
• What happens when you push something along a rough surface?

  You do work against frictional forces
• How is energy transferred when work is done against friction?

  Energy is transferred to kinetic energy of the object
• What are the key concepts related to work and energy in physics?

  • Work is done when a force moves an object
  • Energy is transferred during work
  • Efficiency measures useful energy transfer
  • Frictional forces require work against them
• What does efficiency equal in energy transfer?

  Useful energy transferred by device
• What happens when you push something along a surface?

  You do work against frictional forces
• What is being transferred when an object starts moving?

  Energy is transferred to kinetic energy
• What happens to some energy during movement?

  Some energy is transferred to thermal energy
• How does friction affect the overall temperature of an object?

  It causes the overall temperature to increase
• What is power defined as?

  The rate of energy transfer
• What is the unit of power?

  The watt (W)
• How is power related to work done?

  Power is work done per second
• If an object has a power of 600 W, how much energy does it transfer per second?

  600 J of energy
• What does a higher power indicate about an object?

  More work is done per second
• How do you calculate power from work done and time taken?

  • Power (P) = Work done (E) / Time taken (t)
  • Units: P in watts (W), E in joules (J), t in seconds (s)
• If a motor does 4.8 kJ of work in 2 minutes, what is its power output?

  40 W
• How do you convert kJ to J for power calculations?

  1 kJ = 1000 J
• How do you convert minutes to seconds for power calculations?

  1 minute = 60 seconds
• What is the power output of a heater that transfers twice as much energy as a 600 W heater?

  1200 W
• What should you ensure when using equations for power calculations?

  Use the correct units for each variable
• What is the formula for power in terms of energy and time?

  Power = Energy / Time
• If a heater has a power of 600 W, how much energy does it transfer in 1 minute?

  36,000 J
• What does it mean if a device has a power rating of 1200 W?

  It transfers 1200 J of energy per second
• How does the power of a heater compare to that of a motor doing the same work?

  The heater transfers more energy per second
• What is the relationship between power and work done per second?

  Power increases with more work done
• Why is it important to use the correct units in power calculations?

  To ensure accurate results in calculations
• If a device does 4.8 kJ of work in 120 seconds, what is its power output?

  40 W