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Topic
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Displacement
Vectors
Kinematics
Graphs
Energy
Power
Springs
Shadows
Field of Vision
Colors
Concave mirrors
Convex mirrors
Refraction
Lenses
Optical Power
Slides Minutes
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Energy is the capacity to do work
Just like money is the capacity to purchase
There are three types of work that can be done.
(We see the object going faster)
(We see the object going higher)
(We can feel the heat and hear the sound)
In an idealIf system,
there
is being
no friction
and thusnot
nobeing
work is
done
an object
is not
accelerated,
raised,
to overcome
friction
(no
energy
and
there is no
friction
(ideal),
noloss).
work is done.
Accelerate
Raise
Overcome friction
“Constant velocity”
f
The force must be
parallel to the
distance.
Accelerate
Raise
Overcome friction
“Constant velocity”
The vertical component
makes the object lighter
by 86.7 N.
f = 50.0 N
100 N Cos 60
Since the object is moved at constant velocity, the work (energy)
goes to overcome friction and the energy is lost.
Accelerate
Raise
Overcome friction
“Constant velocity”
The vertical component
makes the object lighter
by 64.3 N.
f = 76.6 N
100 N Cos 40
Since the object is moved at constant velocity, the work (energy)
goes to overcome friction and the energy is lost.
Accelerate
Raise
Overcome friction
In this case, all the applied force goes to do the work
and it is the most efficient method to pull the object.
If the object is moved at constant velocity, the work (energy)
goes to overcome friction and the energy is lost.
If the object is accelerated, the work (energy)
goes to the object in the form of kinetic energy.
No friction (no energy loss)
Example
(1 N)(100 m) = 100 J
Energy in
100 J in
IMA = 100
100 J out
Energy out
(100 N)(1 m) = 100 J
As illustrated below, there are two families of simple machines
each family consists of three types of machines:
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Don’t confuse weight with mass!
A hammer falls from a scaffold and 1.5 s later strikes
the ground with a kinetic energy of 157.5 J.
What is the weight of the hammer?
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Work Slide: 5. 1
In flattening the ground of a tennis court, Robert uses a 20 kg
roller as illustrated below.
If Robert pushes the roller a distance of 10 m with an applied
force of 200 N, how much work does he do? .
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Work Slide: 5. 2
In flattening the ground of a tennis court, Robert uses a 20 kg
roller as illustrated below.
If Robert pulls the roller a distance of 10 m with an applied
force of 200 N, how much work does he do?
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Work Slide: 5. 3
In flattening the ground of a tennis court, Robert uses a 20 kg
roller as illustrated below.
Pushing
Pulling
Which is easier to do, push or pull the roller?
It is easier to pull since in pulling the vertical component
of the pull is upward thereby reducing the weight.
However, it is more effective to push the roller as the
vertical component will increase the weight.
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Kinetic Energy Slide: 5. 4
A 20 g bullet has a velocity of 25 000 cm/s. Calculate its
Convert
grams to kilograms
Convert cm/s to m/s
kinetic energy.
20 g = 0.02 kg
25 000 cm/s = 250 m/s
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Kinetic Energy Slide: 5. 5
An object having a mass of 5 kg is traveling at 6 m/s.
It accelerates to a velocity of 12 m/s. How much work
was done to accelerate the object?
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Potential Energy Slide:
5. 6
A 2 kg mass, moving horizontally at 10 m/s, slides up a
frictionless incline as illustrated in the diagram below.
How high up the incline does the mass rise?
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Potential Energy Slide:
5. 7
Starting with an initial velocity of 10 m/s, a 2 kg object slides
down a frictionless shoot as illustrated in the following diagram.
How high up the incline does the mass travel before coming
to a stop?
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Machines Slide: 5. 8
Which one of the following simple machines cannot be used
to lift a 100 kg load by applying a force less than 980 N?
A) I
B) I and III
C) I and IV
D) I, II and IV
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Machines Slide: 5. 9
Betty uses the hoist illustrated on the right
to raise a mass of 200 kg.
If she can pull the rope 5.0 metres in a time
of 10 seconds, what is Betty’s power output?
Note: Disregard friction.
A) 17.0 W
I.M.A. = 6 (6 ropes)
B) 100 W
C) 163 W
D) 980 W
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Machines Slide: 5. 10
Which two of the following simple machines have the
same ideal mechanical advantage?
1
2
IMA = 5
3
A) 1 and 2
IMA = 4
4
B) 1 and 4
C) 2 and 4
D) 3 and 4
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… and good luck!