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.

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.

An object moving to the right collides with a stationary object. The two objects stick together. What happens to the total momentum of the objects after the collision?

The total momentum of the objects after the collision is the same as the total momentum before the collision.

An object moving to the right collides with a stationary object. The two objects stick together. What happens to the velocity of the objects after the collision?

After the collision, the objects stick together, so they move in the same direction (to the right) with the same velocity .

True or False? If two objects move towards each other with the same speed before a collision, they will always move away from each other with the same speed after the collision.

False. The only quantity that is the same before and after a collision is the total momentum . The final speed of each object depends on its mass.

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Momentum (AQA GCSE Combined Science: Trilogy: Physics): Flashcards

Exam code: 8464

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Define momentum.

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Cards in this collection (19)

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.
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.
An object moving to the right collides with a stationary object. The two objects stick together.
What happens to the total momentum of the objects after the collision?
The total momentum of the objects after the collision is the same as the total momentum before the collision.
An object moving to the right collides with a stationary object. The two objects stick together.
What happens to the velocity of the objects after the collision?
After the collision, the objects stick together, so they move in the same direction (to the right) with the same velocity.
True or False?
If two objects move towards each other with the same speed before a collision, they will always move away from each other with the same speed after the collision.
False.
The only quantity that is the same before and after a collision is the total momentum. The final speed of each object depends on its mass.

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