What sign convention is used to determine the direction of an object's momentum?

The initial direction of motion is usually assigned as positive. Motion in the opposite direction gives a negative momentum.

Momentum is a .......... quantity, meaning it has both magnitude and direction.

Momentum is a vector quantity, meaning it has both magnitude and direction.

How do you convert a mass given in grams, or a velocity given in km s -1 , into SI units before calculating momentum?

Mass in grams: divide by 1000 to get kg Velocity in km s -1 : multiply by 1000 to get m s -1

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

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

Define the principle of conservation of momentum .

The total momentum before a collision is equal to the total momentum after a collision, provided no external force acts.

Define a closed (or isolated ) system, in the context of momentum.

A closed or isolated system is one that is not affected by external forces . In such a system, total momentum is conserved.

Distinguish between external and internal forces on a system, and give an example of each.

External forces : act on a system from outside, e.g. friction, weight Internal forces : exchanged between particles within the system, e.g. tension in a string

When a swimmer dives forwards from a stationary boat, the boat moves .......... to conserve momentum.

When a swimmer dives forwards from a stationary boat, the boat moves backwards to conserve momentum.

True or False? The principle of conservation of momentum applies to any collision, even when an external force acts on the system.

False. The principle only applies when no external force acts on the system; the system must be closed (isolated).

What happens to the sign of an object's velocity if it rebounds after a collision?

It changes from positive (before, in the initial direction of motion) to negative (after, having reversed direction).

A .......... force acting over a long time has the same effect as a large force acting over a short time.

A small force acting over a long time has the same effect as a large force acting over a short time.

Why can a hailstone exert a greater force on an umbrella than a raindrop travelling at the same speed?

A hailstone has a greater mass , so it produces a greater change in momentum (impulse) on impact than a raindrop, requiring more force to be exerted by the umbrella to stop it.

Explain why a cricket fielder moves their hands backwards when catching a fast-moving ball.

Moving the hands back increases the contact time over which the ball's momentum changes. Since the impulse (change in momentum) is fixed, a longer time reduces the force exerted on the fielder's hands, lowering the risk of injury.

True or False? Impulse and force are measured in the same SI unit.

False. Impulse is measured in newton seconds (N s) , while force is measured in newtons (N) .

How do you find the impulse from a force-time graph that is a curve?

Count the squares underneath the curve.

How do you find the impulse from a force-time graph made up of straight lines?

Split the graph into sections (e.g. rectangles, right-angled triangles, trapeziums) and find the sum of the areas of each section.

The impulse delivered by a varying force is equal to the area under a .......... -time graph.

The impulse delivered by a varying force is equal to the area under a force -time graph.

True or False? A graph showing a large force acting for a short time always has a smaller impulse than a graph showing a small force acting for a long time.

False. Impulse is equal to the area under the graph . A large force over a short time can produce the same impulse as a small force over a long time, if the areas under the two graphs are equal.

Define an elastic collision.

An elastic collision is one in which kinetic energy is conserved (as well as momentum, which is conserved in all collisions).

Define an inelastic collision.

An inelastic collision is one in which kinetic energy is not conserved , although momentum is still conserved.

How do you determine whether a collision is elastic or inelastic?

Compare the total kinetic energy before and after the collision. If it is unchanged, the collision is elastic ; if it has decreased, the collision is inelastic .

In an inelastic collision, the colliding objects typically .......... together and move with a common velocity.

In an inelastic collision, the colliding objects typically stick together and move with a common velocity.

What name is given to an event, such as a gun firing a bullet, in which a single object separates into two objects moving apart?

An explosion (involving recoil ).

True or False? Momentum is conserved in an elastic collision but not in an inelastic collision.

False. Momentum is conserved in both elastic and inelastic collisions; it is kinetic energy that is not conserved in an inelastic collision.

When two objects stick together after a collision, how should the resulting object be treated in calculations?

As a single object with mass equal to the sum of the two individual objects' masses.

A LevelPhysicsAQAFlashcardsMechanics & MaterialsLinear Momentum & Conservation

Linear Momentum & Conservation (AQA A Level Physics): Flashcards

Exam code: 7408

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FrontLinear Momentum
Define momentum.

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Cards in this collection (31)

Define momentum.
Momentum is the product of an object's mass and velocity: $p = m v$ . It is a vector quantity, measured in kg m s^-1.
What sign convention is used to determine the direction of an object's momentum?
The initial direction of motion is usually assigned as positive. Motion in the opposite direction gives a negative momentum.
Momentum is a .......... quantity, meaning it has both magnitude and direction.
Momentum is a vector quantity, meaning it has both magnitude and direction.
How do you convert a mass given in grams, or a velocity given in km s^-1, into SI units before calculating momentum?
- Mass in grams: divide by 1000 to get kg
- Velocity in km s^-1: multiply by 1000 to get m s^-1
True or False?
A heavier object always has greater momentum than a lighter, faster-moving object.
False.
Momentum depends on both mass and velocity, so a light, fast-moving object (e.g. a tennis ball) can have the same momentum as a much heavier, slower object (e.g. a brick).
Define the principle of conservation of momentum.
The total momentum before a collision is equal to the total momentum after a collision, provided no external force acts.
Define a closed (or isolated) system, in the context of momentum.
A closed or isolated system is one that is not affected by external forces. In such a system, total momentum is conserved.
Distinguish between external and internal forces on a system, and give an example of each.
- External forces: act on a system from outside, e.g. friction, weight
- Internal forces: exchanged between particles within the system, e.g. tension in a string
When a swimmer dives forwards from a stationary boat, the boat moves .......... to conserve momentum.
When a swimmer dives forwards from a stationary boat, the boat moves backwards to conserve momentum.
Write the equation relating the momenta of two objects, A and B, before and after a collision.
$p_{A i} + p_{B i} = p_{A f} + p_{B f}$
where $p_{A i}$ and $p_{B i}$ are the initial momenta of A and B, and $p_{A f}$ and $p_{B f}$ are their final momenta.
True or False?
The principle of conservation of momentum applies to any collision, even when an external force acts on the system.
False.
The principle only applies when no external force acts on the system; the system must be closed (isolated).
What happens to the sign of an object's velocity if it rebounds after a collision?
It changes from positive (before, in the initial direction of motion) to negative (after, having reversed direction).
Define impulse.
Impulse is the product of the force applied and the time for which it acts: $I m p u l s e = F Δ t$ , measured in newton seconds (N s). It is a vector quantity.
State the equation for impulse in terms of change in momentum.
$I m p u l s e = Δ p = m v - m u$
where m = mass, v = final velocity, u = initial velocity.
A .......... force acting over a long time has the same effect as a large force acting over a short time.
A small force acting over a long time has the same effect as a large force acting over a short time.
Why can a hailstone exert a greater force on an umbrella than a raindrop travelling at the same speed?
A hailstone has a greater mass, so it produces a greater change in momentum (impulse) on impact than a raindrop, requiring more force to be exerted by the umbrella to stop it.
Explain why a cricket fielder moves their hands backwards when catching a fast-moving ball.
Moving the hands back increases the contact time over which the ball's momentum changes. Since the impulse (change in momentum) is fixed, a longer time reduces the force exerted on the fielder's hands, lowering the risk of injury.
True or False?
Impulse and force are measured in the same SI unit.
False.
Impulse is measured in newton seconds (N s), while force is measured in newtons (N).
Show that the newton second (N s), the unit of impulse, is equivalent to the unit of momentum.
Since 1 N = 1 kg m s^-2:
$N s = {kg m s}^{- 2} \times s = {kg m s}^{- 1}$
which is the unit of momentum.
Define impulse, in terms of a force-time graph.
Impulse is equal to the area under a force-time graph, since $I m p u l s e = F o r c e \times Δ t$ .
How do you find the impulse from a force-time graph that is a curve?
Count the squares underneath the curve.
How do you find the impulse from a force-time graph made up of straight lines?
Split the graph into sections (e.g. rectangles, right-angled triangles, trapeziums) and find the sum of the areas of each section.
The impulse delivered by a varying force is equal to the area under a ..........-time graph.
The impulse delivered by a varying force is equal to the area under a force-time graph.
True or False?
A graph showing a large force acting for a short time always has a smaller impulse than a graph showing a small force acting for a long time.
False.
Impulse is equal to the area under the graph. A large force over a short time can produce the same impulse as a small force over a long time, if the areas under the two graphs are equal.
Define an elastic collision.
An elastic collision is one in which kinetic energy is conserved (as well as momentum, which is conserved in all collisions).
Define an inelastic collision.
An inelastic collision is one in which kinetic energy is not conserved, although momentum is still conserved.
How do you determine whether a collision is elastic or inelastic?
Compare the total kinetic energy before and after the collision. If it is unchanged, the collision is elastic; if it has decreased, the collision is inelastic.
In an inelastic collision, the colliding objects typically .......... together and move with a common velocity.
In an inelastic collision, the colliding objects typically stick together and move with a common velocity.
What name is given to an event, such as a gun firing a bullet, in which a single object separates into two objects moving apart?
An explosion (involving recoil).
True or False?
Momentum is conserved in an elastic collision but not in an inelastic collision.
False.
Momentum is conserved in both elastic and inelastic collisions; it is kinetic energy that is not conserved in an inelastic collision.
When two objects stick together after a collision, how should the resulting object be treated in calculations?
As a single object with mass equal to the sum of the two individual objects' masses.

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