This document covers momentum in A-Level Physics. It includes three key objectives: understanding Newton's third law of motion, defining momentum as p=mv, and knowing the principle of conservation of linear momentum. Additional skills gained from this lesson include estimation, laying out answers clearly, and performing derivations. The document then provides example problems and tasks for students to work through related to momentum, collisions, explosions, and applying momentum in real-world contexts like car crashes.

1. A –Level Physics:
Momentum

2. Objectives: (samespecpoints….differenttopic…)
• Spec point: 20. know and understand Newton’s third law of
motion and know the properties of pairs of forces in an
interaction between two bodies
• Spec point: 21 understand that momentum is defined as p = mv
• Spec point: 22 know the principle of conservation of linear
momentum, understand how to relate this to Newton’s laws of
motion and understand how to apply this to problems in one
dimension
Additional Skills Gained:
• Calculation- specific to momentum
• Estimation

3. Lesson Link:
A Fermi (or is it?)
Atruckcomestoa1000mlongbridgeandstopsrightbefore
goingontoittoreadasign.Thesignsaysthatthemaximum
weightthebridgecanholdis4tons(3628kg),whichisthe
exactweightofthetruck.Sothetruckstartsdrivingonthe
bridge.Abouthalfwayoverthebridgealittlebirdlandsonthe
topofthetruck.Doesthebridgebreak?

4. Protect the egg! Independent. S
In pairs (or groups of three) you have one week to
plan how you would protect an egg that will be
dropped from a height. You can use only: bubble
wrap, card and basic accompaniments. Be creative!
This plan must include:
1. A detailed diagram with labels of each
component used to protect the egg
2. An outline of the problems that need to be
overcome with relevant reference to scientific
theory
3. A justification for the use of each component
(i.e. how in terms of physics would this help the
egg survive?)
4. A free-body diagram explaining the forces acting
on the egg at each point of its journey
Each team member must write up an individual plan
(expected length= 1-2 sides of A4)

5. Task: Today’s notes should be written in the form of
diagrams that have been annotated
You thought you were done with me
didn’t you? Not so fast…

6. Principle of Conservation of Momentum
Task: What does the Principle of Conservation of
Momentum state?
Oh…you already know this? You learnt it in
GCSE?....tell me what I said then…

7. Principle of Conservation of Momentum
Task: When you have watched the demonstration on the
air track, write a small paragraph explaining what you saw
The total momentum before an event (collision
or explosion) is equal to the momentum after
*Warning*
“Total” means if there is more than one object,
then you add the momentums of the
individual objects together.

8. 0ms-1
20ms-1
Collisions
? ms-1
500kg 400kg
BEFORE
AFTER
? Kg
Task: How fast are the cars going after the collision?

9. 0ms-1
20ms-1
Collisions
500kg 400kg
BEFORE
AFTER
? ms-1
? Kg
Momentum before (P(b))
Object 1: m x v = 10000 kgms-1
Object 2: m x v = 0 kgms-1
Total: 10000 + 0
= 10000kgms-1
Momentum before (P(b)) = Momentum after(P(a))
1) Total mass is now 900kg
2) p= m x v
3) 10000kgms-1 = 900kg x v
4) v= 10000/900 = 11.1ms-1
So momentum of both objects together
must equal 10000kgms-1
When solving these, use your estimation skills
and common sense. If the two objects collide,
then the speed of them when attached
together will likely be LESS than the fastest
object.

10. Let’s make things a
little trickier…
Collision practice…
1) A 0.5 kg trolley is pushed at a velocity of 1.2ms-1 into a
stationary trolley B of mass 1.5 kg. The two trolleys stick to
each other after the impact. Calculate the velocity they
travel at.
2) A 1000 kg rail wagon moving at a velocity of 5.0ms-1 on a
level track collides with a 2ms-1 1500 kg wagon. The two
wagons move together after the collision. Calculate the
velocity they travel at.
Try them out!

11. 12ms-1
20ms-1
Collisions: Head on!
? ms-1
500kg 400kg
BEFORE
AFTER
? Kg
What information missing from the diagram above?
-
What velocity are the cars travelling at after the collision?
Always make the forward (to
the right) direction positive!

12. 20ms-1
Collisions: Head on
BEFORE
AFTER
? ms-1
? Kg
Momentum before (P(b))
Object 1: m x v = 10000 kgms-1
Object 2: m x v = -6000 kgms-1
Total: 10000 + (-6000)
= 4000kgms-1
Momentum before (P(b)) = Momentum after(P(a))
1) Total mass is now 900kg
2) p= m x v
3) 6000kgms-1 = 900kg x v
4) v= 10000/900 = 6.67ms-1
So momentum of both objects together
must equal 6000kgms-1
12ms-1
500kg
-
500kg
FORWARD

13. Collision practice 2…
1) A car of mass 1000 kg travels east at 30ms-1 and collides with a 3000kg
truck traveling west at 20ms-1. What velocity do they have assuming they
attach to one another?
2) A railway truck of mass 800 kg moving with a constant velocity of -5 ms-1,
collides and couples with another railway truck of mass 650 kg which is
travelling at 16ms-1. Calculate the common velocity (v) with which the
coupled trucks move off after the collision
3) A bowling ball of mass 6kg travelling at 3ms-1 collides with a stationary pin.
They stick to one another and travel off at 2.4ms-1 , what is the mass of
the bowling pin?
4) If one tennis ball was to be thrown upward with 25ms-1 and I dropped one
downward (to collide and stick), what would both balls do according to the
principle? What will they actually do and why?
Try them out!
I doth loveth this
game..

14. My dastardly tennis ball
problem…mwahaha
If one tennis ball was to be thrown upward with 25ms-1 and
dropped one downward (to collide and stick), what would both
balls do according to the principle? What will they actually do and
why?
According to the principle, momentum would be conserved
therefore both balls would travel upward together
We know this doesn’t happen…..but why?
Collisions only obey the principle when there are no external
forces at play. In this situation, the gravitational pull of the
earth on the balls (weight) is interfering!

15. 0ms-1
400ms-1
Explosions! BAM KAPOW BOOOOM
Gun: 1.2kg
Bullet: 0.005kg
BEFORE
AFTER
Task: What is the velocity of the gun?
Momentum before (P(b)) = Momentum after(P(a))
So momentum of both objects together
must equal 0kgms-1

16. 0ms-1
400ms-1
Explosions! BAM KAPOW BOOOOM
Gun: 1.2kg
Bullet: 0.005kg
BEFORE
AFTER
Task: If the bullet is speeding off, how is momentum conserved?
Which law supports this?
Momentum before (P(b))
Object 1 + 2:
m x v = 1.205kg x 0
Total = 0kgms-1
https://www.youtube.com/watch?v=8c3aHHG7_Q0

17. Explosion practice…
1) Katniss uses a bow and arrow to hunt a deer. Her bow has a mass of
2.5kg and her arrow of 0.02kg. Upon release, the bow moves
backward with a velocity of 0.75ms-1 , what velocity does the arrow
have?
2) Two trolleys are attached with a spring. When released, trolley B
(1.5kg) moves forward with a velocity of 8ms-1 , trolley B of mass 1kg
will move at what velocity?
3) Explain with reference to both the conservation of momentum and
newton’s laws, the following:
A mother and daughter are on a skating rink. The mother pushes the
stationary daughter and they both move in opposite directions with
different speeds.
Try them out!
I doth loveth this
game..

18. Momentum in context…
https://www.youtube.com/watch?v=d7iYZPp2zYY
Using what you have learnt so far…explain why the use
of air bags, seatbelts and crumple zones helps protect
drivers and passengers in a car crash. Do this in the
form of an ANNOTATED diagram.
𝒎𝒗 − 𝒎𝒖
𝒕
F=
So to reduce the force, you
need to INCREASE the time
taken for the MOMENTUM to
change

19. Protect the egg! Independent. S
In pairs (or groups of three) you have one week
to plan how you would protect an egg that will
be dropped from a height. You can use only:
bubble wrap, card and basic accompaniments.
Be creative! This plan must include:
1. A detailed diagram with labels of each
component used to protect the egg
2. An outline of the problems that need to be
overcome with relevant reference to
scientific theory
3. A justification for the use of each
component (i.e. how in terms of physics
would this help the egg survive?)
Each team member must write up an individual
plan.

20. Objectives:
• Spec point: 20. know and understand Newton’s third law of
motion and know the properties of pairs of forces in an
interaction between two bodies
• Spec point: 21 understand that momentum is defined as p = mv
• Spec point: 22 know the principle of conservation of linear
momentum, understand how to relate this to Newton’s laws of
motion and understand how to apply this to problems in one
dimension
Additional Skills Gained:
• Estimation
• Laying out answers
• Derivation