Describe the energy transfer that takes place when the brakes of a moving vehicle are applied.

Work done by the friction force between the brakes and the wheels reduces the kinetic energy of the vehicle and raises the thermal energy store of the brakes.

What happens to the kinetic energy of a car as it is brought to rest by its brakes?

It is transferred away by the work done against friction, mostly heating the brakes and the surroundings.

How does increasing the braking force affect the deceleration of a vehicle?

A greater braking force produces a greater deceleration.

AQA GCSE Combined Science Physics 8464

Atomic Structure

Topic overview The structure of an atom Mass number, atomic number and isotopes From the plum pudding model to the nuclear model Chadwick, the neutron, and comparing the models Radioactive decay and nuclear radiation Nuclear equations Half-lives and the random nature of radioactive decay Radioactive contamination

Electricity

Topic overview Circuit symbols, electrical charge and current Current, resistance and potential difference Ohmic conductors, filament lamps, diodes and thermistors Light-dependent resistors, and investigating resistance Current and potential difference in series and parallel Constructing circuits, and calculating in series circuits Direct and alternating potential difference, and mains electricity Power and efficiency Appliances, and the energy transferred by electrical work Power, and the power ratings of domestic appliances The National Grid

Energy

Topic overview Energy stores and systems Kinetic energy Elastic and gravitational potential energy Energy changes in systems Power Energy transfers in a system The main energy resources, renewable and non-renewable Environmental impact and trends in energy use

Forces

Topic overview Scalars, vectors, forces and the resultant force Gravity Work done and energy transfer Stretching, compressing, and the spring constant Linear and non-linear extension, and work done on a spring Distance, displacement and speed The speed of sound, and the distance-speed-time equation Velocity and the distance-time relationship Acceleration, deceleration and velocity-time graphs Area under a velocity-time graph, and the uniform acceleration equation Newton's First Law Newton's Second and Third Laws Stopping distance and reaction time Factors affecting braking distance Braking force, deceleration and the dangers of stopping quickly

Magnetism and Electromagnetism

Topic overview Poles of a magnet Magnetic fields around a magnet The compass, and plotting a magnetic field Electromagnetism

Particle Model of Matter

Topic overview Density of materials Changes of state and internal energy Temperature changes in a system and specific heat capacity Changes of state and specific latent heat Particle motion in gases

Waves

Topic overview Transverse and longitudinal waves, and the wave equation Wave properties, and refraction at a boundary Types and uses of electromagnetic waves Radio waves, and the hazards of ultraviolet, X-rays and gamma rays

Forces

Braking force, deceleration and the dangers of stopping quickly

3 things to know
Physics Paper 2

Overview

The energy transfer when brakes are applied, how speed affects the braking force needed, how braking force sets deceleration, and the dangers of overheating brakes, skidding and large forces on passengers.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why do the brakes of a vehicle get hot when it stops?

Key term

How does the speed of a vehicle affect the braking force needed to stop it within a fixed distance?

Key term

Two identical cars stop in the same distance, but one is travelling twice as fast as the other. Which needs the greater braking force?

Questions from this subtopic

Each one with the model answer underneath.

1
Describe the energy transfer that takes place when the brakes of a moving vehicle are applied.
Model answer
Work done by the friction force between the brakes and the wheels reduces the kinetic energy of the vehicle and raises the thermal energy store of the brakes.
2
Why do the brakes of a vehicle get hot when it stops?
Model answer
Friction between the brakes and the wheels does work on the brakes, so their temperature rises.
3
What happens to the kinetic energy of a car as it is brought to rest by its brakes?
Model answer
It is transferred away by the work done against friction, mostly heating the brakes and the surroundings.
4
How does the speed of a vehicle affect the braking force needed to stop it within a fixed distance?
Model answer
The greater the speed, the greater the braking force needed.
5
Two identical cars stop in the same distance, but one is travelling twice as fast as the other. Which needs the greater braking force?
Model answer
The faster car, because more kinetic energy must be removed over the same distance.
6
How does increasing the braking force affect the deceleration of a vehicle?
Model answer
A greater braking force produces a greater deceleration.

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