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2
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• Displacement, on the other hand, is not only distance travelled, but also direction
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Velocity formula:

•

“inherits” its direction from
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Acceleration formula:

Air resistance is the frictional force air exerts on a moving object
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Therefore, the distance travelled by the
object will decrease
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They can only be
used if the acceleration a is CONSTANT
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Topic 2 Page 6

Projectile Motion
A projectile is an object that has been given an initial velocity by some sort of short-lived force, and then
moves through the air under the influence of gravity
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Suppose you are riding your bike
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In other words, the velocity of a particle depends on the reference
frame of whoever is observing or measuring the velocity
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(ignore air resistance for this question) [3 marks]
d) Describe the effect of air resistance on the falling rescue package
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2 - Forces

Topic 2 Page 10

Object as point particles
•
•
•
•

Be able to:
• Know what a force is
• Know what weight is

A force is a push or a pull measured in Newtons
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Weight is a force that goes down towards the centre of the earth
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This is called the normal
force
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Normal is always sketched perpendicular to the contact surface
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Tension is sketched at whatever angle is given
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Topic 2 Page 12

Problems involving forces
1
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3
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Break down the forces into x and y components
Add all the x components with each other and y components with each other
Use pythagoras to solve for the resultant force
Use sin or cos to find the angle

Topic 2 Page 13

Translational Equilibrium

Be able to:
• Know what translational equilibrium is

• Translational Equilibrium is when an object is either at rest or moving at constant velocity
• The resultant force of an object has to be 0 for it to be in equilibrium

Topic 2 Page 14

Newton's Laws of motion
Newton's First Law
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same
direction unless acted upon by an unbalanced force
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The greater the mass (of the object being accelerated)
the greater the amount of force needed (to accelerate the object)
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Topic 2 Page 15

Be able to:
• Know Newton's laws of motions

Solid Friction

Be able to:

Friction is the force that occurs between two surfaces in contact
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Dynamic friction is when there is movement
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Dynamic Friction:

Static Friction:
(If Ff is bigger, the object will move)

Topic 2 Page 16

• Calculate the net force of an object when its stationary or moving
• Calculate the coefficient of friction

Inclined Plane & Tension

FN

mg
mg

mg
+
mg

T

Topic 2 Page 17

Lifts
Case 1: No Acceleration on Elevator
If the elevator is at rest or moving with a constant speed:
The person pushes down on the scale with a force of
The scales push back up against the person with
So:
Case 2: Going Up & Speeding Up
The elevator and the person are starting from rest at a lower floor
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The elevator floor and scale must push up on the person to accelerate him upward
along with the elevator
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The normal force is thus larger and the reading on the scale is greater than the true weight
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The acceleration of the elevator is downward
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The normal force is thus smaller, so the reading on the
scale is less than the true weight
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The elevator accelerates upward
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The scale pushes upward with extra force on the person to accelerate the person upward
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• The person is accelerating downward with force
• Gravity is acting down on the person
• The scale applies an upward force
So:
(Same equation in case 2)
Case 5: Going down & speeding up
The elevator and the person are initially at rest at a higher floor
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The normal force is thus
smaller, so the reading on the scale is less than the true weight
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All objects in freefall accelerate downward with the same magnitude
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Topic 2 Page 19

Paper 2 Questions
Q1
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The soles and heels of her hiking boots have a
static friction coefficient equal to 1
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a) Show that the steepest slope she can stand on is 45° to the horizontal
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30
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e
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Consider the system of three masses joined by light ropes
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a) If the surface of the table is frictionless, calculate the acceleration of the box
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However if a fly lands on the 80
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What is the static
friction coefficient for the box and table surface? [2 marks]

Topic 2 Page 20

2
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Work is measured in Joules (J)
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is the angle (Parallel is 0, Antiparallel is 180)
One joule is the energy required when a force of one newton acts through a distance of one metre
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2
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4
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It is measured in Joules
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• Identify different types of energy
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• Be able to calculate energy in a system

Types of energy:
Kinetic energy is the energy of a mass in motion
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Elastic (potential) energy is the energy of a deformation in an elastic object
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Remember this

“the total energy of a system never changes
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Topic 2 Page 26

Efficiency
Be able to:
Efficiency is a measure of how much work or energy is conserved in a process
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0 kg, steps off a 10
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The
trampoline stretches and bring Sam to rest 1
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See the photograph below:

Sam at the low point of her bounce 1
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a) How much energy is stored in the stretched fabric of the trampoline when Sam is at rest?
Assume there are no energy losses
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She reaches a height of 7
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How much energy was lost by the stretching trampoline fabric? [2 marks]

Topic 2 Page 28

2
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When net force on a system is zero the total momentum is
constant
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Kinetic energy in terms of momentum

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• Know what momentum is and how to calculate it

Newton's second law in terms of momentum

Collisions
• A collision is an event in which a relatively strong force acts on two or more bodies for a
relatively short time
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An inelastic collision is one where energy is lost
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T graph

Topic 2 Page 33

Paper 2 Questions
Q1:

a) What was the speed of the clay ball before it hit the glider? [3 marks]
b) Was the collision elastic? Give a reason for your answer

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