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 force applied.
• Give an example of work done.

  Work is done on a ball when it is lifted to a height above the ground.
• 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.
• 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 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 formula W = F × s 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.
• If a car applies a force of 500 N and stops after 23 m, what is the work done by the brakes?

  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 the number of Joules equals the number of newton-metres.
• 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 away to the thermal store.
• Calculate the work done when lifting an object with a force of 100 N for a distance of 10 m.

  W = 100 N × 10 m = 1000 N m.
• What type of energy is transferred when lifting an object?

  Energy is transferred to the gravitational potential store of the object.
• What is the gravitational field strength used in the example of lifting a bucket?

  The gravitational field strength is 9.8 N/kg.
• 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.
• How do you calculate the work done on the bucket when it is raised?

  Work = m × g × h, where m is mass, g is gravitational field strength, and h is height.
• Calculate the work done on a 10 kg bucket raised 15 m with a gravitational field strength of 9.8 N/kg.

  Work = 10 kg × 9.8 N/kg × 15 m = 1470 N m.
• What is the relationship between changes in speed and kinetic energy?

  Changes in speed are related to kinetic energy.
• What is the relationship between changes in height and gravitational potential energy?

  Changes in height are related to gravitational potential energy.
• What is the relationship between changes in shape and elastic potential energy?

  Changes in the shape of materials are related to elastic potential energy.
• What is friction?

  Friction is a force that works in opposition to the motion of an object.
• How does friction affect the motion of an object?

  Friction slows down the motion of the object.
• What happens to energy when friction is present?

  Energy is transferred by heating, raising the temperature of the object and its surroundings.
• What causes the rise in temperature when work is done against frictional forces?

  The work done against frictional forces causes a rise in temperature.
• What is air resistance?

  Air resistance is a type of friction that slows the motion of an object.
• How does air resistance transfer energy?

  Energy is transferred by heating due to the work done against air resistance.
• How does air resistance affect a rocket during re-entry?

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