Space time and motion

• What is a scalar quantity?

  A quantity that only has a magnitude.
• What is a vector quantity?

  A quantity that has both a magnitude and a direction.
• What is the difference between speed and velocity?

  Speed is a scalar quantity whereas velocity is a vector quantity.
• What is the difference between distance and displacement?

  Distance is a scalar quantity whereas displacement is a vector quantity.
• How can a vector quantity be represented graphically?

  As an arrow, where the length represents magnitude and the direction indicates direction.
• Is a force a vector or a scalar quantity?

  Vector.
• Give three examples of vector quantities.

  Velocity, displacement, and force.
• If an object moves 3 metres to the left and then 3 metres back to its initial position, what is the object’s total displacement?

  The object has zero displacement.
• Give three examples of scalar quantities.

  Temperature, time, and mass.
• What does the gradient of a distance-time graph represent?

  Velocity.
• What does the gradient of a velocity-time graph represent?

  Acceleration.
• What does the area under a velocity-time graph represent?

  Displacement.
• What is the problem with using an iterative model to model an object’s motion?

  Iterative models assume that no change occurs between the sampled time intervals.
• How can the accuracy of an iterative model be improved?

  By decreasing the time interval.
• What is a vehicle’s stopping distance equal to?

  The sum of its thinking and braking distances.
• What is Newton’s first law?

  A stationary body will remain at rest and a moving body will remain at constant speed, unless acted on by an external force.
• What is the defining equation for Newton’s second law?

  Force = Mass x Acceleration
• If the vehicle’s speed is increased, what can be said about its stopping distance?


  The stopping distance is also increased.
• How can impulse be described?

  Impulse can be described as the change in momentum or as the product of force and the time over which it is applied.
• What does Newton’s third law state?

  Newton’s third law states that every action has an equal and opposite reaction.
• Give a typical range of values for human reaction time.

  0.2 seconds - 0.9 seconds.
• What does the law of the conservation of energy state?

  The law of the conservation of energy states that energy can never be created or destroyed - it can only be transferred between different forms.
• What is done when energy is transferred between different forms?


  Work is done when energy is transferred between different forms.
• Give three things which can affect a driver’s reaction time.

  Tiredness, drugs, and alcohol.
• Give two factors which may affect braking distance.

  Adverse (wet/icy) road conditions and poor tyre or brake conditions.
• What must be done before calculating the work done if the force acts at an angle to the object’s motion?

  The force must be resolved into components, and the component in the direction of motion should then be used.
• 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.
• What is the equation linking work done and power?

  Power = Work Done / Time
• What must be done when dealing with projectile motion questions?

  You should consider the horizontal and vertical components of the projectile’s motion separately.
• 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 is the equation used to calculate the work done by a force?

  Work Done = Force x Distance
• What is the law of the conservation of momentum?

  The total momentum of a system before an event must always equal the total momentum after the event, given no external forces act.
• What is the equation for kinetic energy?

  Kinetic Energy = $\frac{1}{2} \times \text{Mass} \times (\text{Velocity})^2$
• What is the equation for gravitational potential energy?


  Gravitational Potential Energy = Mass x Gravitational Field Strength x Change in Height
• What is the equation for momentum?

  Momentum = Mass x Velocity.
• What unit is used for momentum?


  Kgms^-1
• What is the equation for gravitational potential energy in symbols?


  $\Delta E_p =$$m \times g \times \Delta h$
• Is momentum a scalar or vector quantity?


  Momentum is a vector quantity since it involves velocity and so has a magnitude and direction.
• What do the variables in the equations of motion represent?

  v = final velocity, u = initial velocity, a = acceleration, t = time, s = displacement.
• What does the slope of a position-time graph represent?

  The slope represents the velocity of the object.