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Student calculation sheet
Name .....................................................................
P10.4
Class .................
Date .....................
Momentum
Specification references:


P5.7.1 Momentum is a property of moving objects
MS 1a, 3a, 3b, 3c, 3d
Aims
In this activity you will practise calculating momentum and using the Law of
conservation of momentum in collisions. You will also calculate the rate of
change of momentum or force on an object in a collision. You will look at how this
knowledge contributes to the design of safety devices.
Learning outcomes
After completing this activity, you should be able to:



recall and apply the equation for momentum
determine force resulting from the rate of change of momentum
explain safety features such as air bags, seatbelts, crash mats, cycle helmets,
and cushioned surfaces in playgrounds with reference to impact time /rate of
change of momentum.
Worked example
Two ice hockey players skate towards the puck. The players are travelling in
opposite directions. They collide and fall over, coming to a stop. Using the
information below the diagram, calculate the initial velocity of player B.
© Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original.
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Student calculation sheet
Name .....................................................................
P10.4
Class .................
Date .....................
Step 1 Momentum after the collision  0 kg m/s (both players fall over)
Step 2 Remember that player B is moving to the left so will have a negative
velocity and player A has a positive velocity.
Momentum before the collision  (mass player A  velocity player A) 
(mass player B  velocity player B)
 90  5  85 × v
 450  85v
Step 3 Law of conservation of momentum states
momentum before the collision  momentum after the collision
450  85 × v  0
450 = 85 v
Dividing by 85:
v  5.2 941 176 or 5.29 (3 significant figures).
Player B had a velocity of 5.29 m/s to the left before the collision.
Questions
1
Circle the correct words or phrases to make the following sentences true.
a If the velocity of a moving object doubles, its kinetic energy / momentum
will double.
b If you drop a suitcase out of a moving car, the car’s momentum will
increase / decrease if the speed of the car remains constant.
c When a force acts on an object the momentum of the object changes /
stays the same.
d When two objects collide the total momentum stays the same / changes.
2
Write the numbers of the following four vehicles on the line below, in order of
momentum from lowest to highest.
Truck 1 v  30 m/s
m  3000 kg
Truck 2 v  20 m/s
m  5000 kg
Truck 3 v  15 m/s
m  4500 kg
Truck 4 v  10 m/s
m  4200 kg
lowest momentum ----------------------------------------------- highest momentum
(5 marks)
© Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original.
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Student calculation sheet
Name .....................................................................
3
a
P10.4
Class .................
Date .....................
An ice skater of mass 67 kg is moving to the east at 4 m/s. She collides
with a stationary man of 70 kg and she grabs hold of him to make sure he
doesn’t fall over. What is their final momentum in this inelastic collision,
and in what direction do they travel after the collision? Give your answer to
3 significant figures.
(3 marks)
b
Two ice skaters are practising a lift. They skate directly towards each other.
The woman has a mass of 60 kg and a velocity of 3 m/s towards the east.
The man has a mass of 100 kg and is skating at a velocity of 4 m/s towards
the west. They time it badly and collide and bounce off each other’s
outstretched hands. The woman moves off at a velocity of 5 m/s towards the
west. With what velocity does the man move off and in which direction?
(5 marks)
4
a
A melon is thrown from a tower block. It has a mass of 3 kg and falls with a
constant velocity of 2 m/s. It hits the ground and splits in 0.2 s.
i What is its momentum before impact?
(1 mark)
ii
With what force does it hit the floor?
(1 mark)
b
A second identical melon is thrown from the same tower. This melon is
encased in two cycle helmets which are strapped securely round it. The
melon again falls at 2 m/s but this time the duration of the impact is slowed
to 2 s.
i What force does this melon experience?
(1 mark)
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This resource sheet may have been changed from the original.
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Student calculation sheet
Name .....................................................................
ii
Class .................
P10.4
Date .....................
Why is this protected melon more likely to survive the fall intact?
(1 mark)
iii How do seatbelts and air bags help to keep drivers safe in collisions?
(2 marks)
5
The playground floor under some swings has a rubber safety surface to
prevent accidents.
a A child, with a mass of 45 kg, falls off a swing and hits the ground at a
speed of 5 m/s.
i Calculate the momentum of the child as he hits the ground. Show
clearly how you work out your answer and give the units.
(2 marks)
ii
After hitting the ground, the child slows down and stops in 0.3 s.
Calculate the force exerted by the ground on the child. Show clearly
how you work out your answer and give the units.
(2 marks)
b
One type of rubber tile used to cover the playground surface is shown below.
Explain how the rubber tiles reduce the risk of children being seriously
injured when they fall off the playground equipment.
(3 marks)
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This resource sheet may have been changed from the original.
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Student calculation sheet
Name .....................................................................
P10.4
Class .................
Date .....................
The ‘critical fall height’ is the height that a child can fall and not be expected to sustain a lifethreatening head injury. A new type of tile, made in a range of different thicknesses, was tested in a
laboratory using test dummies and the ‘critical fall height’ measured. Only one test was completed on
each tile. The results are shown in the graph.
The ‘critical fall height’ for playground equipment varies from 0.5 m to 3.0 m.
Suggest two reasons why more tests are needed before this new type of
tile can be used in a playground.
(2 marks)
© Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original.
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