# Physics - Stopping Distances

> Source: https://ollybritton.com/notes/a-level/physics/topics/stopping-distances/ · Updated: 2020-10-08 · Tags: physics, year-1, school

##### What is the formula for _stopping_ distances??
$$
\text{stopping distance} = \text{thinking distance} + \text{braking distance}
$$

##### What affects reaction time in the context of stopping distances??
* Tiredness
* Alcohol
* Drugs
* Other passengers

##### What are the two factors that affect stopping distance??
* Reaction time
* Speed of the vehicle

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

##### What are the three factors that affect braking distance??
* Breaking force
* Mass of vehicle
* Velocity

##### What things can affect the breaking force??
* Break conditions
* Tire conditions
* Road conditions

##### A larger vehicle mass has what affect on braking distance??
A larger breaking distance.

##### When a car is in motion, what's the kinetic energy of the car??
$$
\frac{1}{2} m v^2
$$

##### Where is the kinetic energy of a car transferred to when braking??
Transferred to the thermal store of the breaks and the surroundings.

##### What is the work done by a car when it's breaking??
$$
W = F \times s
$$

##### When a car is breaking and the energy is being calculated by $W = F \times s$, what does $F$ represent??
The breaking force of the car.

##### What are the units for work done??
joules, $J$

##### What must be true about the kinetic energy of a car and the work done when breaking??
They must be equal.

##### What is the formula for the kinetic energy of a car in relation to work done??
$$
\frac{1}{2} m v^2 = F \times s
$$

##### What is the formula for breaking distance involving mass, velocity and breaking force??
$$
\frac{1}{2} m v^2 = F \times s
$$

##### What is the formula for breaking distance involving velocity and acceleration??
$$
\text{breaking distance} = \frac{(initial velocity)^2}{2 \times \text{acceleration}}
$$

##### What does a $2\times$ initial velocity translate to in terms of breaking distance??
$4\times$ the breaking distance.

##### The breaking distance equation involving velocity and acceleration is a special case of which SUVAT equation??
$$
v^2 = u^2 + 2as
$$

##### If a truck is exerts a breaking force of $8700N$ and has a mass of $2300kg$, how could you calculate the acceleration??
$$
\text{8700N}{2300kg} \\\\
F = ma
$$

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