The change in momentum of a body, equal to force × time for a constant force: I = FΔt = Δp

Define force in terms of momentum.

The rate of change of momentum of a body

The impulse equation I = FΔt can only be used when the force is ..........

The impulse equation I = FΔt can only be used when the force is constant

True or False? The impulse on an object acts in the opposite direction to the force that produces it.

False. Impulse is a vector in the same direction as the force acting on the object

Why is the impulse on an umbrella greater in hail than in rain?

Hailstones have a larger mass and bounce back off the umbrella, giving a greater change in momentum , whereas rain droplets splatter and fall off with only a small change in momentum

What is the aim of Core Practical 9: Investigating Impulse?

To determine the change in momentum (impulse) of a trolley caused by a force acting on it

In Core Practical 9, what are the independent and dependent variables?

Independent variable = accelerating (hanging) mass, m Dependent variable = time, t , taken to pass between the two light gates

In Core Practical 9, the ramp is tilted slightly to compensate for ..........

In Core Practical 9, the ramp is tilted slightly to compensate for friction

For each new reading in Core Practical 9, one 10 g mass is moved from the trolley onto the ..........

For each new reading in Core Practical 9, one 10 g mass is moved from the trolley onto the hanger

True or False? Moving a mass onto the hanger increases the total mass of the system in Core Practical 9.

False. Each mass added to the hanger is taken from the trolley , so the total mass of the system stays constant

State the principle of conservation of linear momentum .

The total momentum before a collision equals the total momentum after , provided no external force acts

Momentum is conserved in a collision provided that no .......... acts.

Momentum is conserved in a collision provided that no external force acts.

Why must you define a positive direction when applying conservation of momentum?

Momentum is a vector , so an object moving the opposite way has a negative velocity and momentum — oppositely-directed momenta can cancel out

How is momentum conserved in a 2D collision?

Each component is conserved separately — the sum of horizontal components before = after, and the sum of vertical components before = after

In a 2D collision, the horizontal and vertical .......... of momentum are each conserved separately.

In a 2D collision, the horizontal and vertical components of momentum are each conserved separately.

True or False? When an object reverses direction after a collision, its velocity keeps the same sign in the momentum equation.

False. A change of direction is shown by a change of sign — the velocity (and momentum) becomes negative

What is the aim of Core Practical 10: Investigating Collisions using ICT?

To investigate the conservation of momentum in two directions (2D) using colliding spheres, and to consider whether the collisions are elastic

In Core Practical 10, the digital camera must be positioned directly .......... the collision.

In Core Practical 10, the digital camera must be positioned directly above the collision.

Why is ICT (video and Tracker software) used in Core Practical 10?

The collisions happen too swiftly for the unaided eye to take readings, and ICT generally provides more precise and reliable data

Core Practical 10 uses two spheres of different .......... so their motion can be distinguished.

Core Practical 10 uses two spheres of different diameters so their motion can be distinguished.

How are the momenta represented after analysis in Tracker?

As a vector diagram constructed from the momentum of each sphere recorded before and after the collision

Give one systematic error in Core Practical 10 and how to reduce it.

Parallax error between the camera and the table — position the camera directly above the collision (also accept: misaligned Tracker axes , or an imprecise balance for measuring mass)

True or False? Variations in the table surface that cause a loss or gain of kinetic energy are a systematic error in Core Practical 10.

False. These are random errors, because they vary unpredictably from one collision to the next

Define an elastic collision .

A collision in which kinetic energy is conserved

Define an inelastic collision .

A collision in which kinetic energy is not conserved — some is transferred to other forms such as heat and sound

In both collisions and explosions, .......... is always conserved.

In both collisions and explosions, momentum is always 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 decreases it is inelastic

Why is a head-on collision between two cars inelastic?

Kinetic energy is transferred to heat and sound through crumpling (plastic deformation) of the bodywork, so the total KE after is less than before

True or False? A collision is inelastic only if the two objects stick together.

False. A collision is inelastic whenever kinetic energy is not conserved — the objects do not have to stick together

What type of event does recoil describe, and give an example.

An explosion — for example a gun recoiling after firing a bullet, or an unstable nucleus emitting an alpha particle and a daughter nucleus

The energy-momentum relation is derived by substituting .......... into the kinetic energy equation.

The energy-momentum relation is derived by substituting v = p/m into the kinetic energy equation.

In the equation E k = p²/2m, the symbol p represents the .......... of the particle.

In the equation E k = p²/2m, the symbol p represents the momentum of the particle.

For which types of calculation is the energy-momentum relation especially useful?

The kinetic energy of subatomic particles at non-relativistic speeds, and projectiles or collisions involving large masses

How do you convert an energy from eV into J?

Multiply by 1.6 × 10 -19 , since 1 eV = 1.6 × 10 -19 J

A LevelPhysicsEdexcelFlashcards6. Further MechanicsMomentum & Impulse

Momentum & Impulse (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

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Define impulse.

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Cards in this collection (42)

Define impulse.
The change in momentum of a body, equal to force × time for a constant force: I = FΔt = Δp
Define force in terms of momentum.
The rate of change of momentum of a body
What is the equation for the impulse of a constant force?
$I = F Δ t = Δ p = m v - m u$
where v is final velocity and u is initial velocity
The unit of impulse is ..........
The unit of impulse is N s
The impulse equation I = FΔt can only be used when the force is ..........
The impulse equation I = FΔt can only be used when the force is constant
True or False?
The impulse on an object acts in the opposite direction to the force that produces it.
False.
Impulse is a vector in the same direction as the force acting on the object
Why is the impulse on an umbrella greater in hail than in rain?
Hailstones have a larger mass and bounce back off the umbrella, giving a greater change in momentum, whereas rain droplets splatter and fall off with only a small change in momentum
What is the aim of Core Practical 9: Investigating Impulse?
To determine the change in momentum (impulse) of a trolley caused by a force acting on it
In Core Practical 9, what are the independent and dependent variables?
Independent variable = accelerating (hanging) mass, m
Dependent variable = time, t, taken to pass between the two light gates
In Core Practical 9, the ramp is tilted slightly to compensate for ..........
In Core Practical 9, the ramp is tilted slightly to compensate for friction
Which two expressions for the change in momentum are combined in Core Practical 9?
$Δ p = M (v_{B} - v_{A})$
and
$Δ p = m g t$
A graph of mt against (v_B − v_A) gives a straight line — what does its gradient equal?
The gradient equals $\frac{M}{g}$
where M is the mass of the system and g is the acceleration due to gravity
For each new reading in Core Practical 9, one 10 g mass is moved from the trolley onto the ..........
For each new reading in Core Practical 9, one 10 g mass is moved from the trolley onto the hanger
True or False?
Moving a mass onto the hanger increases the total mass of the system in Core Practical 9.
False.
Each mass added to the hanger is taken from the trolley, so the total mass of the system stays constant
State the principle of conservation of linear momentum.
The total momentum before a collision equals the total momentum after, provided no external force acts
Momentum is conserved in a collision provided that no .......... acts.
Momentum is conserved in a collision provided that no external force acts.
Why must you define a positive direction when applying conservation of momentum?
Momentum is a vector, so an object moving the opposite way has a negative velocity and momentum — oppositely-directed momenta can cancel out
Two objects of equal mass m and speed v travel towards each other. What is their total momentum before colliding?
Zero, because $p_{t o t a l} = m v + (- m v) = 0$
The negative sign shows the objects move in opposite directions
How is momentum conserved in a 2D collision?
Each component is conserved separately — the sum of horizontal components before = after, and the sum of vertical components before = after
In a 2D collision, the horizontal and vertical .......... of momentum are each conserved separately.
In a 2D collision, the horizontal and vertical components of momentum are each conserved separately.
True or False?
When an object reverses direction after a collision, its velocity keeps the same sign in the momentum equation.
False.
A change of direction is shown by a change of sign — the velocity (and momentum) becomes negative
What is the aim of Core Practical 10: Investigating Collisions using ICT?
To investigate the conservation of momentum in two directions (2D) using colliding spheres, and to consider whether the collisions are elastic
In Core Practical 10, the digital camera must be positioned directly .......... the collision.
In Core Practical 10, the digital camera must be positioned directly above the collision.
Why is ICT (video and Tracker software) used in Core Practical 10?
The collisions happen too swiftly for the unaided eye to take readings, and ICT generally provides more precise and reliable data
Core Practical 10 uses two spheres of different .......... so their motion can be distinguished.
Core Practical 10 uses two spheres of different diameters so their motion can be distinguished.
How are the momenta represented after analysis in Tracker?
As a vector diagram constructed from the momentum of each sphere recorded before and after the collision
Give one systematic error in Core Practical 10 and how to reduce it.
Parallax error between the camera and the table — position the camera directly above the collision
(also accept: misaligned Tracker axes, or an imprecise balance for measuring mass)
True or False?
Variations in the table surface that cause a loss or gain of kinetic energy are a systematic error in Core Practical 10.
False.
These are random errors, because they vary unpredictably from one collision to the next
Define an elastic collision.
A collision in which kinetic energy is conserved
Define an inelastic collision.
A collision in which kinetic energy is not conserved — some is transferred to other forms such as heat and sound
In both collisions and explosions, .......... is always conserved.
In both collisions and explosions, momentum is always 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 decreases it is inelastic
Why is a head-on collision between two cars inelastic?
Kinetic energy is transferred to heat and sound through crumpling (plastic deformation) of the bodywork, so the total KE after is less than before
True or False?
A collision is inelastic only if the two objects stick together.
False.
A collision is inelastic whenever kinetic energy is not conserved — the objects do not have to stick together
What type of event does recoil describe, and give an example.
An explosion — for example a gun recoiling after firing a bullet, or an unstable nucleus emitting an alpha particle and a daughter nucleus
State the energy-momentum relation.
$E_{k} = \frac{p^{2}}{2 m}$
where E_k is kinetic energy, p is momentum and m is mass
Derive the energy-momentum relation from $E_{k} = \frac{1}{2} m v^{2}$ and $p = m v$ .
Substitute $v = \frac{p}{m}$ into the kinetic energy equation:
$E_{k} = \frac{1}{2} m {(\frac{p}{m})}^{2} = \frac{1}{2} \frac{p^{2}}{m} = \frac{p^{2}}{2 m}$
The energy-momentum relation is derived by substituting .......... into the kinetic energy equation.
The energy-momentum relation is derived by substituting v = p/m into the kinetic energy equation.
In the equation E_k = p²/2m, the symbol p represents the .......... of the particle.
In the equation E_k = p²/2m, the symbol p represents the momentum of the particle.
For which types of calculation is the energy-momentum relation especially useful?
The kinetic energy of subatomic particles at non-relativistic speeds, and projectiles or collisions involving large masses
How do you convert an energy from eV into J?
Multiply by 1.6 × 10^-19, since 1 eV = 1.6 × 10^-19 J
True or False?
For a fixed momentum, a particle with a larger mass has a larger kinetic energy.
False.
Since $E_{k} = \frac{p^{2}}{2 m}$ , kinetic energy is inversely proportional to mass for a fixed momentum — a larger mass gives a smaller kinetic energy

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