braking and momentum

• What does the graph of force against extension represent for elastic objects?

  Relationship between force and extension
• What law is associated with momentum in the study material?

  Law of conservation of momentum
• What does the law of conservation of momentum state?

  Momentum remains constant in isolated systems
• What are the speeds mentioned for a person walking?

  1.5 m/s, 30 m/s, and 60 m/s
• What do opposite forces refer to in the context of motion?

  Forces acting in opposite directions
• How do the speeds for a person walking vary in Chapter 10?

  • 1.5 m/s
  • 30 m/s
  • 60 m/s
• What is the name given to the distance a vehicle travels to safely come to a stop after the driver has spotted a hazard?

  Stopping distance
• What is thinking distance?

  The distance vehicle travels during driver's reaction time
• What is braking distance?

  The distance vehicle travels once brakes have been applied
• What is the relationship between stopping distance, thinking distance, and braking distance?

  Stopping = thinking distance + braking distance
• Does the speed of a vehicle have a bigger effect on braking distance or thinking distance?

  Braking distance
• Which distance is proportional to the speed of the vehicle?

  Thinking distance
• Which distance increases by an increasing amount as speed increases?

  Braking distance
• What are three factors that can affect the braking distance of a vehicle?

  • Speed of the vehicle
  • Road conditions
  • Condition of brakes and tyres
• What is the definition of one joule of work?

  The work done when 1N of force causes 1m displacement
• Why does the temperature of a vehicle's brakes increase when the brakes are applied?

  Friction transfers energy to thermal energy stores
• What can happen if the braking force used to stop a vehicle is very large?

  Brakes may overheat or the car may skid
• What is the law of conservation of momentum?

  Total momentum before equals total momentum after
• What does $m\Delta v$ stand for?


  Change in momentum
• How is the force acting on an object related to its momentum?

  Force equals rate of change of momentum
• What is the unit for stopping distance?

  Metres (m)
• How does speed affect the kinetic energy of a vehicle?

  Greater speed increases kinetic energy
• What happens to the work done to slow down a vehicle as its mass increases?

  More work is needed to slow it down
• What is the relationship between braking force and stopping distance?

  Greater braking force reduces stopping distance
• How can deceleration be calculated?

  Using $F =$$ma$
• What happens if the braking force is very large?

  The car may skid or lose control
• What is the effect of increasing the time taken for the change in momentum?

  Smaller rate of change of momentum
• How do vehicle safety features help in a crash?

  They increase time for momentum change
• What is the symbol for momentum?

  p
• What is the range of human reaction times?

  0.2s to 0.9s
• What factors can affect reaction time?

  Tiredness, drugs, alcohol, distractions
• How can reaction times be measured?

  Using a computer or ruler drop test
• What is the purpose of the ruler drop test?

  To calculate reaction time
• What should you remember about the unit for stopping distance?

  It is metres (m), not miles
• How does mass affect the braking force needed to stop a vehicle?

  Greater mass requires greater braking force
• What happens to the braking distance if road conditions are poor?

  Braking distance increases
• How does speed affect the work done to stop a vehicle?

  Higher speed means more work to stop
• What is the effect of skidding on braking distance?

  Skidding increases braking distance
• What is the relationship between kinetic energy and speed?

  Kinetic energy is proportional to speed squared
• How does the braking force relate to the energy transferred?

  Braking force times distance equals energy transfer