Work and Energy

• What happens to energy when a force acts on a moving object?

  Energy is transferred, but the total amount remains constant (conservation of energy).
• What is the formula for work done?

  W = FdWork = Force × Distance moved in the direction of the force.
• What is work a measure of?

  Work is a measure of energy transfer (when no energy is lost as heat).
• What forms of energy can an object have due to motion, position, or shape?

  Kinetic energy (motion)Gravitational potential energy (position)Elastic potential energy (deformation)
• What is the equation for kinetic energy?

  KE = 1/2 mv²Where m = mass, v = velocity.
• What is the equation for change in gravitational potential energy?

  ΔPE = mghWhere m = mass, g = gravitational field strength, h = change in height.
• What is Hooke’s Law for force and extension?

  F = kxForce = Spring constant × Extension
• How do you calculate the work done in stretching a spring?

  W = 1/2 FxIt’s the area under a force-extension graph for a linear spring.
• How can energy efficiency of vehicles be improved?

  Reduce air resistance (streamlining)Reduce rolling resistance (efficient tyres)Reduce idling losses (stop-start engines)Reduce inertia (use lighter materials)
• How do car safety features reduce injury in a crash?

  By increasing the time over which momentum changes, reducing the force:AirbagsCrumple zonesSeatbelts(All reduce peak force using the principle F = Δp / t)