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Stopping distance is braking distance and reaction distance.

# Forces - Forces and Braking

This GCSE Physics quiz looks at forces and braking. Understanding braking forces is an important part of being able to drive. Knowing approximately how far it will take you to stop is not just important for yourself, but also for the safety of other road users.

Before we consider the braking force acting on a vehicle, it is necessary to understand what forces are acting on a vehicle. The driving force comes from the engine and this moves it forward. The weight is created by the force of gravity acting on the mass of the vehicle, holding it to the ground. Acting in the opposite direction to the weight is the reaction force. There are two forces acting in opposition to the driving force, the friction with the road and the air resistance. The air resistance is much greater than the friction with the road when a vehicle is in motion.

1.
If a car is travelling at a steady speed, what can be said of the driving and resistive forces acting on the car?
In equilibrium
Driving forces are twice as large as the resistive forces
Resistive forces are twice as large as the driving forces
There are no resistive forces acting on the car at a steady speed
Whenever forces are in equilibrium, motion is either unchanging or the object is stationary
2.
A car stops in 20 m when travelling at 30 kilometers per hour. If the car is travelling at 40 kilometres per hour, how far does the car take to stop?
20m
26m
27m
30m
Some questions regarding braking can be answered by using nothing more complicated than simple ratios to calculate distances
3.
Which of the following statements is true?
The greater the speed of a vehicle, the greater the braking force needed to stop it within a certain distance
The smaller the speed of a vehicle, the greater the braking force needed to stop it within a certain distance
The greater the speed of a vehicle, the less braking force is needed to stop it within a certain distance
The greater the mass of a vehicle, the less braking force is needed to stop it within a certain distance
The driver needs to push the brake pedal harder. This could lead to the dangerous situation where the force of braking locks up the wheels. When this happens, the driver has little control over the vehicle. To avoid this danger, most vehicles are now equipped with anti-locking braking systems
4.
What is braking distance?
The distance travelled in 10 seconds when a car is accelerating
The distance travelled while the brakes are applied
The distance required to accelerate to 100mph
The energy required to stop in a given distance
Faster speeds mean greater braking distances are required. Careful drivers therefore leave more of a gap between their vehicle and the one in front at higher speeds
5.
What is stopping distance?
Braking distance
Reaction time
Braking distance and reaction distance
Reaction distance
The stopping distance is the distance the car will travel in total. This takes into consideration how long it takes a driver to react to a situation and consequently the distance travelled during this period. It also takes into consideration the distance the car takes to stop once the brakes have been applied
6.
If a driver's reaction time is 0.2 s and the braking time when their car is travelling at 10 m/s is 10 s, how far does the car travel before it comes to rest?
50m
51m
52m
53m
At a speed of 10 m/s, the car travels one metre every 0.1 second. With a thinking time of 0.2 seconds, the car will therefore have travelled 2 metres.

You have the initial speed of the car before braking, the final speed after braking (must be 0 m/s since it has stopped) and the time it took to stop the car. You can therefore use the equation s = ½ (v+u) × t to calculate the stopping distance. This is then added to the distance travelled during the thinking time to come up with the answer. You could also use s = ut + ½ at2 but you would then need to take the additional step of calculating the acceleration.

Make sure that you learn the equations of motion linking initial velocity (u), final velocity (v), acceleration (a), displacement (s) and time (t).

7.
What can affect a driver's reaction time?
Drink
Drugs
Tiredness
All of the above
The other factor is distraction - talking to passengers, using their mobile phone, loud music and so on
8.
Which statement is true?
When the brakes are applied, work done by friction between the brake and wheel increases the kinetic energy of the vehicle and decreases the temperature of the brakes
When the brakes are applied, work done by friction between the brake and wheel reduces the kinetic energy of the vehicle and increases the temperature of the brakes
When the brakes are released, work done by friction between the brake and wheel reduces the kinetic energy of the vehicle and increases the temperature of the brakes
When the brakes are applied, work done by friction between the brake and wheel reduces the kinetic energy of the vehicle and decreases the temperature of the brakes
Energy can only be transferred, so the kinetic energy of the car needs to be transferred into another form - in this case the heat in the brakes
9.
What can affect a vehicle's braking distance?
Worn brakes
Worn tyres
All of the above
Braking distance can be severely reduced by any of the above which is why it is important to regularly check for brake and tyre wear. It is also important to leave a larger gap between cars in poorer weather conditions. Speed also affects the braking distance so it is also important to leave a larger gap between cars moving at high speeds
10.
What is the greatest resistive force a car experiences when no braking forces are applied?
Air resistance
Passenger weight
Stones
Rain
This is created as the vehicle collides with air molecules