5.6

• What type of quantity is distance: scalar or vector?


  Distance is a scalar quantity.
• Why does distance not require a specific direction?


  Because it is defined as a scalar quantity.
• If an object moves 3 metres to the left and then 3 metres back, what is its total displacement?


  The object has zero displacement.
• Why is displacement considered a vector quantity?


  Because it involves both magnitude and direction.
• What is a typical value for the speed of sound?


  330 m/s
• What is a typical value for human walking speed?


  1. 5 m/s
• What is a typical value for human running speed?

  3 m/s
• What is a typical value for human cycling speed?

  6 m/s
• What is the equation linking distance, speed, and time?


  Distance = Speed x Time
• What are the appropriate units for distance, speed, and time?

  Distance (m), Speed (m/s), Time (s)
• Why can an object traveling at a constant speed in a circle not have a constant velocity?


  Because the direction is continuously changing.
• How can speed be calculated from a distance-time graph?


  The speed is equal to the gradient of the graph.
• What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?


  Draw a tangent to the curve at the required time and calculate the gradient of the tangent.
• What is the equation for average acceleration of an object?

  Acceleration = (Change in Velocity)/(Time Taken)
• What are the appropriate units for acceleration, velocity, and time?

  Acceleration (m/s²), Velocity (m/s), Time (s)
• How can the distance travelled by an object be calculated from a velocity-time graph?


  It is equal to the area under the graph.
• What is the approximate value for the acceleration of an object in free fall under gravity near the Earth’s surface?


  1. 8 m/s²
• What can be said about the resultant force acting on an object when it is falling at terminal velocity?


  The resultant force is zero.
• What happens to an object at terminal velocity?


  The object is moving at a constant speed and isn’t accelerating.
• State Newton’s first law for a stationary object.


  If the resultant force on a stationary object is zero, the object will remain at rest.
• State Newton’s first law for a moving object.

  If the resultant force on a moving object is zero, the object will remain at constant velocity.
• What can be said about the braking forces and driving forces when a car is travelling at constant velocity?


  The braking forces are equal to the driving forces.
• If an object changes direction but remains at a constant speed, is there a resultant force?


  Yes, there is a resultant force due to the change in direction.
• What does Newton's first law state for a moving object?

  If the resultant force on a moving object is zero, the object will remain at constant velocity.
• What is inertia?

  Inertia is the tendency of an object to continue in its state of rest or uniform motion.
• What is the defining equation for Newton's Second Law?


  Resultant force = Mass x Acceleration (F = ma).
• How can Newton's Second Law be stated in words?

  An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.
• What is inertial mass?

  Inertial mass is a measure of how difficult it is to change a given object's velocity and is the ratio of force over acceleration.
• What symbol is used to represent an approximate value?


  The symbol used to represent an approximate value is ≈.
• What does Newton's Third Law state?

  Whenever two objects interact, the forces that they exert on each other are always equal and opposite.
• What is the stopping distance of a vehicle equal to?


  The stopping distance of a vehicle is equal to the sum of thinking distance and braking distance.
• What happens to the stopping distance if the vehicle's speed is increased?


  The stopping distance is increased with an increase in speed.
• What is a typical range of values for human reaction time?


  A typical range of values for human reaction time is 0.2 seconds - 0.9 seconds.
• What are three factors that can affect a driver's reaction time?


  1. Tiredness 2. Drugs 3. Alcohol
• What are two factors that may affect braking distance?


  1. Adverse (wet/icy) road conditions 2. Poor tyre/brake conditions
• Describe the energy transfers that take place when a car applies its brakes.

  Work is done by the friction force between the brakes and wheel, converting kinetic energy of the wheel to heat dissipated to the surroundings through the brake discs.
• To stop a car in a given distance, if its velocity is increased, what must happen to the braking force applied?


  The braking force must also be increased.
• What are two consequences of a vehicle undergoing very large decelerations?


  1. Kinetic energy converted to heat is very high causing brakes to overheat 2. Loss of control of the vehicle