Forces and Motions

• Does a distance quantity require a specific direction?

  No, it is a scalar quantity.
• What is the total displacement of an object that moves 3 metres left and then 3 metres back?

  The object has zero displacement.
• What type of quantity is displacement?

  Displacement is a vector quantity.
• Why does the object have zero displacement in the previous scenario?

  It starts and ends at the same point.
• 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 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.
• What is the equation for the 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 traveled 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.
• Why is the resultant force zero at terminal velocity?

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

  If the resultant force is zero, it remains at rest.
• State Newton’s first law for a moving object.

  If the resultant force is zero, it remains at constant velocity.
• What can be said about the braking forces and driving forces when a car is traveling 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.
• What is inertia?

  The tendency of an object to continue in its state of rest or uniform motion.
• State the defining equation for Newton’s Second Law.

  Resultant force = Mass x Acceleration
• State Newton’s Second Law in words.

  Acceleration is directly proportional to resultant force and inversely proportional to mass.
• What is inertial mass?

  A measure of how difficult it is to change velocity.
• What is the symbol used to represent an approximate value?

  ≈
• State Newton’s Third Law.

  Forces exerted on each other are equal and opposite.
• What is the stopping distance of a vehicle equal to?

  The sum of thinking distance and braking distance.
• For a given braking distance, what can be said about stopping distance if the vehicle’s speed is increased?

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

  0.2 seconds - 0.9 seconds
• Give three factors which can affect a driver’s reaction time.

  Tiredness, Drugs, Alcohol
• Give two factors which may affect braking distance.

  Adverse road conditions, Poor tyre/brake conditions
• Describe the energy transfers that take place when a car applies its brakes.

  Kinetic energy is converted to heat through friction.
• 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.
• State two consequences of a vehicle undergoing very large decelerations.

  Kinetic energy converted to heat is very high, Loss of control of the vehicle.