Work Done & Energy Transfer

• What is work done when an object is moved over a distance?

  Work is done when a force is applied in the direction of the object's displacement.

  
• What happens if a force is applied to an object but there is no movement?

  No work is done if there is no movement despite the applied force.
• Give an example of work done.

  Work is done on a ball when it is lifted to a height above the ground.
• What is an example of work done by a bird?

  Work is done when a bird flies through the air.
• What role does air resistance play when a bird flies?

  Air resistance does work against the bird as it flies through the air.
• How does the weight of a ball relate to work done when it is lifted?

  The weight of the ball does work over a distance equal to the height it is lifted.
• How is the amount of work done related to force and distance?

  The amount of work done is related to the size of the force and the distance moved in the direction of the force.

  
• What is the formula to calculate work done?

  W = F × s
• What do the symbols in the work formula represent?

  W = work done in Joules (J), F = force in Newtons (N), s = distance in metres (m).

  
• How do you calculate the work done by the brakes of a car?

  Work = F × s, where F is the force applied and s is the distance.
• Calculate the work done by the brakes if a force of 500 N stops a car after 23 m.

  Work = 500 N × 23 m = 11,500 J.

  
• What are the units for work?

  Work is measured in joules (J) or newton-metres (N m).
• What is the relationship between joules and newton-metres?

  1 J = 1 N m, meaning they are equivalent units for work.
• What happens whenever work is done?

  Energy is transferred from one store to another.
• How is energy transferred when a force acts in the direction of movement?

  The object gains energy, transferring it to its kinetic store.
• What happens when a force acts in the opposite direction to movement?

  The object loses energy, transferring it to the thermal store of the object and surroundings.
• Calculate the work done when lifting an object with a force of 100 N for a distance of 10 m.

  Work = 100 N × 10 m = 1000 N m.
• What is the energy transferred when lifting an object with a force of 100 N for a distance of 10 m?

  Energy transferred is equal to the work done, which is 1000 J.
• Describe the energy transfer involved in raising a bucket out of a well.

  Work is done by the woman as she pulls the bucket up, transferring energy to its gravitational potential store.

  
• Calculate the energy transferred to a bucket with a mass of 10 kg raised 15 m in a gravitational field of 9.8 N/kg.

  Energy transferred = 10 kg × 9.8 N/kg × 15 m = 1470 J.
• What is friction and how does it affect motion?

  Friction is a force that opposes motion, slowing down the object.
• What happens to energy when friction is present?

  Energy is transferred by heating, raising the temperature of the object and surroundings.
• How does work done against friction affect temperature?

  The work done against friction causes a rise in temperature of the object and surroundings.
• What causes the transfer of energy to the thermal store when an object moves?

  Imperfections at the interface between the object and the surface cause energy transfer to the thermal store.
• What is air resistance?

  Air resistance is a type of friction that slows the motion of an object as particles bump into it.
• How does air resistance affect energy transfer?

  Energy is transferred by heating due to work done against air resistance.
• What happens to a rocket's return module due to air resistance?

  The return module heats up due to work done by air resistance as it travels through the atmosphere.