Physics - Stopping Distances

OCR A-Level Physics 2022

Created: October 08, 2020 | Read markdown | About these notes | View in context | Study these flashcards |

Stopping distance and its components

What is the formula for _ stopping _ distances?

stopping-distance-formula
\[\text{stopping distance} = \text{thinking distance} + \text{braking distance}\]

What affects reaction time in the context of stopping distances?

factors-affecting-reaction-time
  • Tiredness
  • Alcohol
  • Drugs
  • Other passengers

What are the two factors that affect stopping distance?

factors-affecting-stopping-distance
  • Reaction time
  • Speed of the vehicle

Thinking distance

Assuming a constant velocity ($v$) during reaction time, what is the formula for thinking distance?

thinking-distance-formula
\[s = vt\]

Braking distance factors

What are the three factors that affect braking distance?

factors-affecting-braking-distance
  • Braking force
  • Mass of vehicle
  • Velocity

What things can affect the braking force?

factors-affecting-braking-force
  • Brake conditions
  • Tire conditions
  • Road conditions

A larger vehicle mass has what effect on braking distance?

mass-increases-braking-distance

A larger braking distance.

Energy and work in braking

When a car is in motion, what’s the kinetic energy of the car?

kinetic-energy-of-car
\[\frac{1}{2} m v^2\]

Where is the kinetic energy of a car transferred to when braking?

kinetic-energy-transfer-when-braking

Transferred to the thermal store of the brakes and the surroundings.

What is the work done by a car when it’s braking?

work-done-when-braking
\[W = F \times s\]

When a car is braking and the energy is being calculated by $W = F \times s$, what does $F$ represent?

f-is-braking-force

The braking force of the car.

What are the units for work done?

units-of-work-done

joules, $J$

What must be true about the kinetic energy of a car and the work done when braking?

kinetic-energy-equals-work-done

They must be equal.

What is the formula for the kinetic energy of a car in relation to work done?

kinetic-energy-work-equation
\[\frac{1}{2} m v^2 = F \times s\]

Braking distance formulae

What is the formula for braking distance involving mass, velocity and braking force?

braking-distance-energy-equation
\[\frac{1}{2} m v^2 = F \times s\]

What is the formula for braking distance involving velocity and acceleration?

braking-distance-suvat-form
\[\text{breaking distance} = \frac{(initial velocity)^2}{2 \times \text{acceleration}}\]

What does a $2\times$ initial velocity translate to in terms of braking distance?

double-velocity-quadruples-braking-distance

$4\times$ the braking distance.

The braking distance equation involving velocity and acceleration is a special case of which SUVAT equation?

braking-distance-from-suvat
\[v^2 = u^2 + 2as\]

If a truck exerts a braking force of $8700N$ and has a mass of $2300kg$, how could you calculate the acceleration?

acceleration-from-braking-force
\[\text{8700N}{2300kg} \\\\ F = ma\]


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