Why does a small force acting over a long time have the same effect as a large force acting over a short time?

Because impulse depends on both the size of the force and the time it acts for. The same impulse (change in momentum) can be produced by a small force over a long time or a large force over a short time.

Why is impulse a vector quantity?

Because it is proportional to force , which is a vector. Impulse acts in the same direction as the force that produces it.

When rain hits an umbrella, the droplets splatter and fall off with only a small change in momentum. When hail hits an umbrella, the hailstones bounce back off it instead. Explain why the impulse on the umbrella is greater in hail than in rain.

Hailstones bounce back , reversing their velocity, so they undergo a larger change in momentum than raindrops, which simply stop. Since impulse equals the change in momentum, the impulse (and the force needed to hold the umbrella steady) is greater in hail than in rain.

The unit of impulse is .......... .

The unit of impulse is N s (newton seconds).

True or False? The equation I = FΔt can be used to calculate impulse for any force, even one that changes with time.

False. The equation I = FΔt is only valid for a constant force. Impulse quantifies the effect of a force acting over a time interval, but a varying force requires a different approach (e.g. the area under a force–time graph).

Define interrupt card .

An interrupt card is a card of known length attached to the trolley that breaks the light beam of a light gate , allowing the time (and hence velocity) of the trolley to be measured as it passes.

What is the independent variable in this practical?

The accelerating mass , m — the mass placed on the hanger.

What is the dependent variable in this practical?

The time , t , taken for the trolley to pass between the two light gates.

State three variables that must be controlled during this experiment.

Overall mass of the system (trolley + accelerating masses) Tilt angle of the ramp Trolley and ramp used Size of interrupter card

Why is the ramp tilted slightly in this experiment?

To compensate for friction , so the trolley travels at approximately constant velocity when no accelerating force is applied.

Why must a mass moved from the trolley to the hanger be transferred rather than simply removed?

To keep the total mass of the system (trolley + masses) constant throughout the experiment, so only the accelerating force changes between readings.

True or False? In this practical, the velocity and time of the trolley are read directly by eye using a stopwatch.

False. The velocity and time are measured using light gates connected to a computer or datalogger, which is more precise and reliable than reading by eye.

Define the principle of conservation of linear momentum .

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

Why can momentum have a negative value?

Because momentum is a vector quantity. If an object reverses direction after a collision, its velocity — and therefore its momentum — becomes negative relative to the chosen positive direction.

Explain how the conservation of momentum is applied to a collision in two dimensions.

Momentum is resolved into horizontal and vertical components . Each component is conserved separately — the sum of horizontal components before the collision equals the sum after, and likewise for the vertical components.

Linear momentum is the momentum of an object that only moves in a .......... .

Linear momentum is the momentum of an object that only moves in a straight line .

True or False? In a 2D collision, only the total speed of the system needs to be conserved, not its direction.

False. Momentum is a vector , so both the horizontal and vertical components of momentum must be conserved separately — not just the overall speed.

Tracker is video analysis software (recommended by Edexcel) used to perform frame-by-frame analysis of the spheres' motion, allowing their velocities and momenta to be calculated from a recorded video of the collision.

Why is ICT (video analysis software) used in this experiment rather than direct observation?

Because the collision happens too quickly for the unaided eye to take accurate readings, and ICT generally provides more precise and reliable data .

What two pieces of data must be entered into Tracker before it can analyse a collision?

The mass and diameter of each sphere.

How should the axes be oriented before using Tracker to analyse the moving sphere's velocity?

So that the velocity of the moving sphere lies along one of the axes .

A systematic error in this experiment is .......... error, caused by the camera not being directly above the table.

A systematic error in this experiment is parallax error, caused by the camera not being directly above the table.

State one random error that could occur in this experiment.

The collision event happening between video frames , so it is not captured (accept: variations in the table surface causing friction/slope effects, or the sphere failing to travel far enough to strike the second sphere).

True or False? This practical uses two spheres of the same diameter to keep the experiment fair.

False. The practical uses spheres of two different diameters (ball bearings are ideal), not the same diameter.

Define an elastic collision .

A collision in which kinetic energy is conserved (as well as momentum). The colliding objects do not stick together — they move away from each other afterwards.

Define an inelastic collision .

A collision in which kinetic energy is not conserved (though momentum is always conserved). The colliding objects commonly stick together afterwards.

Is momentum conserved in an inelastic collision?

Yes. Momentum is always conserved in any collision or explosion — only kinetic energy conservation distinguishes elastic from inelastic collisions.

Explain why a head-on collision between two cars is considered inelastic.

Kinetic energy is transferred to other forms during the collision — mainly crumpling (plastic deformation of the bodywork), as well as heat and sound . Since the total kinetic energy before the collision does not equal the total kinetic energy after, the collision is inelastic.

When two objects collide and stick together, the resulting object should be treated as a single mass equal to the .......... of the two individual masses.

When two objects collide and stick together, the resulting object should be treated as a single mass equal to the sum of the two individual masses.

True or False? An explosion, such as a gun recoiling after firing a bullet, does not conserve momentum because the gun and bullet end up moving apart.

False. Momentum is still conserved in an explosion. If the system starts at rest, the total momentum remains zero — the gun and bullet gain equal and opposite momenta.

For what two types of calculation is the energy-momentum relation particularly useful?

Subatomic particles travelling at non-relativistic speeds (much slower than light) Projectiles and collisions involving large masses

International A Level (IAL)PhysicsEdexcelFlashcards4. Further Mechanics, Fields & ParticlesMomentum & Impulse

Momentum & Impulse (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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Cards in this collection (39)

Define impulse.
Impulse is the change in momentum of an object.
$I = F Δ t = Δ p = m v - m u$
Why does a small force acting over a long time have the same effect as a large force acting over a short time?
Because impulse depends on both the size of the force and the time it acts for. The same impulse (change in momentum) can be produced by a small force over a long time or a large force over a short time.
Why is impulse a vector quantity?
Because it is proportional to force, which is a vector. Impulse acts in the same direction as the force that produces it.
When rain hits an umbrella, the droplets splatter and fall off with only a small change in momentum. When hail hits an umbrella, the hailstones bounce back off it instead. Explain why the impulse on the umbrella is greater in hail than in rain.
Hailstones bounce back, reversing their velocity, so they undergo a larger change in momentum than raindrops, which simply stop. Since impulse equals the change in momentum, the impulse (and the force needed to hold the umbrella steady) is greater in hail than in rain.
The unit of impulse is ...........
The unit of impulse is N s (newton seconds).
True or False?
The equation I = FΔt can be used to calculate impulse for any force, even one that changes with time.
False.
The equation I = FΔt is only valid for a constant force. Impulse quantifies the effect of a force acting over a time interval, but a varying force requires a different approach (e.g. the area under a force–time graph).
Define interrupt card.
An interrupt card is a card of known length attached to the trolley that breaks the light beam of a light gate, allowing the time (and hence velocity) of the trolley to be measured as it passes.
What is the independent variable in this practical?
The accelerating mass, m — the mass placed on the hanger.
What is the dependent variable in this practical?
The time, t, taken for the trolley to pass between the two light gates.
State three variables that must be controlled during this experiment.
- Overall mass of the system (trolley + accelerating masses)
- Tilt angle of the ramp
- Trolley and ramp used
- Size of interrupter card
Why is the ramp tilted slightly in this experiment?
To compensate for friction, so the trolley travels at approximately constant velocity when no accelerating force is applied.
A graph of mt against (v_B − v_A) gives a straight line with gradient equal to ...........
A graph of mt against (v_B − v_A) gives a straight line with gradient equal to $\frac{M}{g}$ .
Why must a mass moved from the trolley to the hanger be transferred rather than simply removed?
To keep the total mass of the system (trolley + masses) constant throughout the experiment, so only the accelerating force changes between readings.
True or False?
In this practical, the velocity and time of the trolley are read directly by eye using a stopwatch.
False.
The velocity and time are measured using light gates connected to a computer or datalogger, which is more precise and reliable than reading by eye.
Define the principle of conservation of linear momentum.
The total momentum before a collision equals the total momentum after a collision, provided no external force acts.
Why can momentum have a negative value?
Because momentum is a vector quantity. If an object reverses direction after a collision, its velocity — and therefore its momentum — becomes negative relative to the chosen positive direction.
Two objects of equal mass m and equal speed v move directly towards each other and collide. What is the total momentum of the system before the collision?
Zero. The two momenta are equal and opposite:
$p_{t o t a l} = m v + (- m v) = 0$
Explain how the conservation of momentum is applied to a collision in two dimensions.
Momentum is resolved into horizontal and vertical components. Each component is conserved separately — the sum of horizontal components before the collision equals the sum after, and likewise for the vertical components.
Linear momentum is the momentum of an object that only moves in a ...........
Linear momentum is the momentum of an object that only moves in a straight line.
True or False?
In a 2D collision, only the total speed of the system needs to be conserved, not its direction.
False.
Momentum is a vector, so both the horizontal and vertical components of momentum must be conserved separately — not just the overall speed.
Define Tracker.
Tracker is video analysis software (recommended by Edexcel) used to perform frame-by-frame analysis of the spheres' motion, allowing their velocities and momenta to be calculated from a recorded video of the collision.
Why is ICT (video analysis software) used in this experiment rather than direct observation?
Because the collision happens too quickly for the unaided eye to take accurate readings, and ICT generally provides more precise and reliable data.
What two pieces of data must be entered into Tracker before it can analyse a collision?
The mass and diameter of each sphere.
How should the axes be oriented before using Tracker to analyse the moving sphere's velocity?
So that the velocity of the moving sphere lies along one of the axes.
A systematic error in this experiment is .......... error, caused by the camera not being directly above the table.
A systematic error in this experiment is parallax error, caused by the camera not being directly above the table.
State one random error that could occur in this experiment.
The collision event happening between video frames, so it is not captured (accept: variations in the table surface causing friction/slope effects, or the sphere failing to travel far enough to strike the second sphere).
True or False?
This practical uses two spheres of the same diameter to keep the experiment fair.
False.
The practical uses spheres of two different diameters (ball bearings are ideal), not the same diameter.
Define an elastic collision.
A collision in which kinetic energy is conserved (as well as momentum). The colliding objects do not stick together — they move away from each other afterwards.
Define an inelastic collision.
A collision in which kinetic energy is not conserved (though momentum is always conserved). The colliding objects commonly stick together afterwards.
Is momentum conserved in an inelastic collision?
Yes. Momentum is always conserved in any collision or explosion — only kinetic energy conservation distinguishes elastic from inelastic collisions.
Explain why a head-on collision between two cars is considered inelastic.
Kinetic energy is transferred to other forms during the collision — mainly crumpling (plastic deformation of the bodywork), as well as heat and sound. Since the total kinetic energy before the collision does not equal the total kinetic energy after, the collision is inelastic.
When two objects collide and stick together, the resulting object should be treated as a single mass equal to the .......... of the two individual masses.
When two objects collide and stick together, the resulting object should be treated as a single mass equal to the sum of the two individual masses.
True or False?
An explosion, such as a gun recoiling after firing a bullet, does not conserve momentum because the gun and bullet end up moving apart.
False.
Momentum is still conserved in an explosion. If the system starts at rest, the total momentum remains zero — the gun and bullet gain equal and opposite momenta.
Define the energy-momentum relation.
$E_{k} = \frac{p^{2}}{2 m}$
It links the kinetic energy E_k of a particle to its momentum p and mass m.
Derive the energy-momentum relation, starting from $E_{k} = \frac{1}{2} m v^{2}$ and $p = m v$ .
Substituting $v = \frac{p}{m}$ into $E_{k} = \frac{1}{2} m v^{2}$ gives:
$E_{k} = \frac{1}{2} m {(\frac{p}{m})}^{2} = \frac{p^{2}}{2 m}$
For what two types of calculation is the energy-momentum relation particularly useful?
- Subatomic particles travelling at non-relativistic speeds (much slower than light)
- Projectiles and collisions involving large masses
An alpha particle is made up of two protons and two neutrons, each of mass 1.67 × 10^-27 kg. Calculate the mass of an alpha particle.
$m_{α} = 2 m_{p} + 2 m_{n} = 2 (1.67 \times 10^{- 27}) + 2 (1.67 \times 10^{- 27}) = 6.68 \times 10^{- 27} kg$
The energy-momentum relation is derived by substituting v = .......... into the kinetic energy equation $E_{k} = \frac{1}{2} m v^{2}$ .
The energy-momentum relation is derived by substituting v = p/m into the kinetic energy equation $E_{k} = \frac{1}{2} m v^{2}$ .
True or False?
The energy-momentum relation $E_{k} = \frac{p^{2}}{2 m}$ can only be used for particles travelling close to the speed of light.
False.
It is used for non-relativistic particles (travelling much slower than light) and for large-mass projectiles and collisions — not for relativistic speeds.

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