momentum

• What is the equation used to calculate an object’s momentum?

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

  kgm/s (kilogram metres per second)
• In a closed system, what can be said about the momentum before and after a collision?

  The total momentum before and after are equal.
• What is the equation linking change in momentum, force, and time?

  Force x Time = Change in Momentum
• How can you measure human reaction times?

  Using the ruler drop test.
• Why is it important that the 0cm mark is at the bottom in the ruler drop test?

  So you can obtain the distance directly without having to calculate it.
• 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 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?

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

  1. Tiredness 2. Drugs 3. Alcohol
• Give two factors which 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, converting kinetic energy to heat.
• 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.

  1. Brakes may overheat 2. Loss of control of the vehicle
• what is an equation linking kinetic energy and work done by the brakes 


  1/2 x m x v2 = braking force x braking distance