Stopping Distances (Edexcel GCSE Physics): Flashcards
Exam code: 1PH0
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Define stopping distance.
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Cards in this collection (27)
Define stopping distance.
Stopping distance is the total distance travelled during the time it takes for a car to stop in response to an emergency.
What is the equation linking stopping distance, thinking distance and braking distance?
Stopping distance = Thinking distance + Braking distance.
For a given braking force, the greater the ______ of a vehicle, the greater its stopping distance.
For a given braking force, the greater the speed of a vehicle, the greater its stopping distance.
Why do heavy vehicles need a larger force to produce the same deceleration as lighter vehicles?
By Newton's second law, F = ma, so for the same acceleration a greater mass requires a greater force.
Explain why overheating brakes can be dangerous.
A vehicle's kinetic energy is converted to thermal energy in the brakes. If the brakes get too hot, they can fail and become less effective at stopping the car.
True or False?
A large deceleration can only damage the vehicle, not injure the passengers.
False.
A large deceleration can cause injuries such as whiplash, and can also make the vehicle harder to control.
In which direction does the resultant force act on a car and its passengers as they decelerate to a stop?
The resultant force acts in the opposite direction to the direction of motion, which is why deceleration is often given a negative value.
Define reaction time.
Reaction time is a measure of how much time passes between seeing something and reacting to it.
What is the typical reaction time range for an alert person?
0.2 to 0.9 seconds.
Describe the ruler-drop method for measuring reaction time.
Person A holds a 30 cm ruler vertically above Person B's open hand and releases it unexpectedly. Person B catches it as soon as they see it move, and the ruler is marked at the point it was caught to measure the distance fallen.
In the ruler-drop method, the ______ the distance the ruler falls, the longer the reaction time.
In the ruler-drop method, the greater the distance the ruler falls, the longer the reaction time.
True or False?
The ruler-drop method directly measures a person's reaction time in seconds.
False.
The method measures the distance the ruler falls. This can be used to calculate a time, but a time is not measured directly.
Give an example of a situation in which a person needs to be alert and ready to react quickly.
An athlete waiting for the start of a race.
Define braking distance.
Braking distance is the distance travelled by a car under the braking force, i.e. while it is slowing down.
Define thinking distance.
Thinking distance is the distance travelled by a car from when a driver realises they need to brake to when they apply the brakes.
State three factors, other than speed, that can increase a car's braking distance.
Worn tyres or poor brakes (vehicle condition), wet or icy roads (road condition), and greater vehicle mass.
How does braking distance change if a car's velocity doubles?
It increases by a factor of four, since braking distance is proportional to velocity squared.
Reaction distance = speed of the car × driver's ______.
Reaction distance = speed of the car × driver's reaction time.
Name three factors that can increase a driver's thinking distance.
Tiredness, distractions (e.g. using a mobile phone), and intoxication (alcohol or drugs).
True or False?
Thinking distance is directly proportional to a car's speed.
True.
A graph of thinking distance against speed is a straight line through the origin, showing direct proportionality.
How is thinking distance related to a car's speed?
Thinking distance is directly proportional to speed, e.g. doubling the speed doubles the thinking distance.
How is braking distance related to a car's speed?
Braking distance is proportional to speed squared, e.g. doubling the speed increases the braking distance by a factor of four.
The braking distance equation shows that the work done by the braking force equals the loss of the car's ______ energy.
The braking distance equation shows that the work done by the braking force equals the loss of the car's kinetic energy.
A car's braking distance at 50 mph is 38 m. Estimate its braking distance at 100 mph.
152 m (38 × 2² = 38 × 4), since braking distance is proportional to velocity squared.
A car's thinking distance at 50 mph is 15 m. Estimate its thinking distance at 100 mph.
30 m (15 × 2), since thinking distance is directly proportional to speed.
True or False?
The equation for braking distance remains accurate at very high speeds.
False.
At very high speeds, brakes get hot and become less effective, reducing the braking force and increasing the braking distance further.
True or False?
According to the Highway Code, the stopping distance of a car travelling at 60 mph is about 73 m. Of this, the braking distance is 18 m, and the thinking distance is 55 m.
False.
For a car travelling at 60 mph, the stopping distance is 73 m, the thinking distance is 18 m, and the braking distance is 55 m.
Thinking distance is directly proportional to a car's speed.
Braking distance is directly proportional to a car's speed squared.
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