What are the units of momentum?

Kilogram metres per second (kg m/s) — the product of the units for mass (kg) and velocity (m/s).

What is the momentum of an object at rest, and why?

Zero , because velocity ( v ) = 0, so p = mv = 0.

An object's momentum changes if it accelerates or decelerates, changes ______ , or its ______ changes.

An object's momentum changes if it accelerates or decelerates, changes direction , or its mass changes.

Why does a large momentum make it difficult to change an object's direction of travel?

Momentum keeps an object moving in the same direction , so a large momentum requires a larger force (or a longer time) to change that direction.

In the exam, which directions are conventionally taken as positive?

Right and upwards are usually taken as positive , with left and downwards taken as negative — though the choice is up to the candidate.

True or False? A heavier object always has more momentum than a lighter, faster-moving object.

False. Momentum depends on both mass and velocity, so a lighter, faster object (e.g. a tennis ball) can have the same momentum as a heavier, slower object (e.g. a brick).

Define conservation of momentum .

In a closed system , the total momentum before an event is equal to the total momentum after the event.

What is meant by a "closed system" in momentum conservation?

A system where energy is constant and there are no external forces acting (e.g. no friction).

What is the overall momentum of two equal-mass objects moving directly towards each other at the same speed?

Zero , because momentum is a vector, so their equal, opposite momenta cancel out .

The total momentum ______ a collision = the total momentum ______ the collision.

The total momentum before a collision = the total momentum after the collision.

What should you draw first when tackling a conservation of momentum question, according to examiner guidance?

A diagram showing the masses, velocities and directions before and after the event.

True or False? Momentum is only conserved if no external forces act on the system.

True. Conservation of momentum applies to a closed system , which by definition has no external forces acting on it.

What quantity is always conserved in a collision?

Momentum is always conserved in a collision.

If kinetic energy is not conserved in a collision, what might it be converted into instead?

It may be converted into heat , sound , or elastic potential energy , among other forms.

The total momentum ______ the collision must equal the total momentum ______ the collision for momentum to be conserved.

The total momentum before the collision must equal the total momentum after the collision for momentum to be conserved.

True or False? When a 1 kg object travelling at 3 m/s collides and sticks to a stationary 2 kg object, the combined mass afterwards is 3 kg.

True. The combined mass is the sum of the two masses: 1 kg + 2 kg = 3 kg .

Define change in momentum .

Change in momentum = final momentum − initial momentum .

What is meant by Δt in the force–momentum equation?

Δ t is the change in time , i.e. the time taken for the force to change the momentum.

From which two physics principles can the force–momentum equation be derived?

Newton's second law and the definition of acceleration .

Force and momentum are both ______ quantities, so they can be either positive or ______ values.

Force and momentum are both vector quantities, so they can be either positive or negative values.

True or False? Force is defined as the rate of change of momentum.

True. When a force acts on a moving (or moveable) object, it causes acceleration or deceleration — a change in momentum — and force is the rate of this change.

Define a crumple zone .

A crumple zone is a part of a vehicle's exterior designed to crush or crumple in a controlled way during a collision, increasing the time over which the vehicle comes to rest and lowering the impact force .

How does increasing the contact time of a collision affect the force of impact?

Increasing the contact time decreases the force of impact, since force is the rate of change of momentum.

Name three vehicle safety features designed to increase the contact time of a collision.

Crumple zones , seat belts , and airbags .

How do seat belts help reduce injury in a collision?

Seat belts stretch slightly , increasing the time for the passenger's momentum to reach zero, which reduces the force on them.

Crash mats are thick and soft to offer ______ of the force created by a person landing on them.

Crash mats are thick and soft to offer shock absorption of the force created by a person landing on them.

Why can a child in a gymnasium use a thinner crash mat than an adult?

Because a child has a lower mass , so their impact produces a smaller change in momentum, requiring less contact time to reduce.

True or False? Safety features completely prevent injury in all collisions.

False. Safety features are intended to reduce the chance of serious injury but do not completely prevent it in all cases.

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Momentum (AQA GCSE Physics): Flashcards

Exam code: 8463

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Cards in this collection (31)

Define momentum.
Momentum (p) is the product of an object's mass and velocity: $p = m v$
What are the units of momentum?
Kilogram metres per second (kg m/s) — the product of the units for mass (kg) and velocity (m/s).
What is the momentum of an object at rest, and why?
Zero, because velocity (v) = 0, so p = mv = 0.
An object's momentum changes if it accelerates or decelerates, changes ______, or its ______ changes.
An object's momentum changes if it accelerates or decelerates, changes direction, or its mass changes.
Why does a large momentum make it difficult to change an object's direction of travel?
Momentum keeps an object moving in the same direction, so a large momentum requires a larger force (or a longer time) to change that direction.
In the exam, which directions are conventionally taken as positive?
Right and upwards are usually taken as positive, with left and downwards taken as negative — though the choice is up to the candidate.
True or False?
A heavier object always has more momentum than a lighter, faster-moving object.
False.
Momentum depends on both mass and velocity, so a lighter, faster object (e.g. a tennis ball) can have the same momentum as a heavier, slower object (e.g. a brick).
Define conservation of momentum.
In a closed system, the total momentum before an event is equal to the total momentum after the event.
What is meant by a "closed system" in momentum conservation?
A system where energy is constant and there are no external forces acting (e.g. no friction).
What is the overall momentum of two equal-mass objects moving directly towards each other at the same speed?
Zero, because momentum is a vector, so their equal, opposite momenta cancel out.
The total momentum ______ a collision = the total momentum ______ the collision.
The total momentum before a collision = the total momentum after the collision.
What should you draw first when tackling a conservation of momentum question, according to examiner guidance?
A diagram showing the masses, velocities and directions before and after the event.
A 990 kg car travelling at 10 m/s collides with a stationary 4200 kg van. What is the total momentum of the system before the collision?
$p = m v = 990 \times 10 = 9900 kg m/s$
The van's momentum is zero since it is at rest, so the total is 9900 kg m/s.
True or False?
Momentum is only conserved if no external forces act on the system.
True.
Conservation of momentum applies to a closed system, which by definition has no external forces acting on it.
What quantity is always conserved in a collision?
Momentum is always conserved in a collision.
If kinetic energy is not conserved in a collision, what might it be converted into instead?
It may be converted into heat, sound, or elastic potential energy, among other forms.
The total momentum ______ the collision must equal the total momentum ______ the collision for momentum to be conserved.
The total momentum before the collision must equal the total momentum after the collision for momentum to be conserved.
A 1 kg object travelling at 3 m/s collides with a stationary 2 kg object, and they stick together. What is their combined velocity after the collision?
Using $p_{b e f o r e} = p_{a f t e r}$ : $1 \times 3 = 3 \times v$ , so $v = 3 \div 3 = 1 m/s$
True or False?
When a 1 kg object travelling at 3 m/s collides and sticks to a stationary 2 kg object, the combined mass afterwards is 3 kg.
True.
The combined mass is the sum of the two masses: 1 kg + 2 kg = 3 kg.
Define change in momentum.
Change in momentum = final momentum − initial momentum.
What is meant by Δt in the force–momentum equation?
Δt is the change in time, i.e. the time taken for the force to change the momentum.
From which two physics principles can the force–momentum equation be derived?
Newton's second law and the definition of acceleration.
Force and momentum are both ______ quantities, so they can be either positive or ______ values.
Force and momentum are both vector quantities, so they can be either positive or negative values.
True or False?
Force is defined as the rate of change of momentum.
True.
When a force acts on a moving (or moveable) object, it causes acceleration or deceleration — a change in momentum — and force is the rate of this change.
Define a crumple zone.
A crumple zone is a part of a vehicle's exterior designed to crush or crumple in a controlled way during a collision, increasing the time over which the vehicle comes to rest and lowering the impact force.
How does increasing the contact time of a collision affect the force of impact?
Increasing the contact time decreases the force of impact, since force is the rate of change of momentum.
Name three vehicle safety features designed to increase the contact time of a collision.
Crumple zones, seat belts, and airbags.
How do seat belts help reduce injury in a collision?
Seat belts stretch slightly, increasing the time for the passenger's momentum to reach zero, which reduces the force on them.
Crash mats are thick and soft to offer ______ of the force created by a person landing on them.
Crash mats are thick and soft to offer shock absorption of the force created by a person landing on them.
Why can a child in a gymnasium use a thinner crash mat than an adult?
Because a child has a lower mass, so their impact produces a smaller change in momentum, requiring less contact time to reduce.
True or False?
Safety features completely prevent injury in all collisions.
False.
Safety features are intended to reduce the chance of serious injury but do not completely prevent it in all cases.

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