Download Science 1.9 Demonstrate understanding aspects of mechanic

WSC 2013
WSC Science
Year 11
Revision Workbook
2013
Demonstrate understanding of
aspects of mechanics
Name ....................................................................
Teacher ................................................................
WSC 2013
Achievement Standard: Science 1.9
Demonstrate understanding aspects of mechanic
Achievement Standard: AS90940
Credits: 4
Assessment: External
This achievement standard involves demonstrating understanding of aspects of
mechanics and may include using methods when solving related problems.
Achievement Criteria
Achievement
Achievement with
Merit
Achievement with
Excellence
 Demonstrate
understanding of
aspects of mechanics.
 Demonstrate in-depth  Demonstrate
understanding of
comprehensive
aspects of mechanics.
understanding of aspects
of mechanics.
Explanatory Notes
1
This achievement standard is derived from The New Zealand Curriculum,
Learning Media, Ministry of Education, 2007, Level 6. It is aligned with the
Physical Inquiry and Physics Concepts achievement objectives in the Physical
World strand and the Communicating in Science achievement objective in the
Nature of Science strand, and is related to the material in the Teaching and
Learning Guide for Science, Ministry of Education, 2010 at
http://seniorsecondary.tki.org.nz.
2
Demonstrate understanding of aspects of mechanics typically involves
providing evidence that shows awareness of how simple facets of phenomena,
concepts or principles relate to given situations. This may include using
methods for solving problems involving aspects of mechanics.
3
Demonstrate in-depth understanding of aspects of mechanics typically involves
providing evidence that shows how or why phenomena, concepts or principles
relate to given situations.
4
Demonstrate comprehensive understanding of aspects of mechanics typically
involves providing evidence that shows how or why phenomena, concepts and
principles are connected in the context of given situations. Statements must
demonstrate understanding of connections between concepts.
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5
Evidence may be written, mathematical, graphical or diagrammatic.
6
Aspects of mechanics will be limited to a selection from the following:
 Distance, speed, interpretation of distance and speed time graphs, average
acceleration and deceleration in the context of everyday experiences such
d
v
as journeys, sport, getting going. The relationships v =
.
a
t
t
 Mass, weight and the acceleration due to gravity, balanced and unbalanced
forces, in the context of everyday experiences such as being stationary,
moving at constant speed, accelerating. The relationship Fnet = ma.
 Force and pressure in the context of everyday experiences. The
F
relationship P =
.
A
 Work and power, gravitational potential energy, kinetic energy, and the
conservation of mechanical energy in free fall situations in the context of
everyday experiences such as sports performance, dropping things, tossing
balls. The relationships EP = mgh EK =
7
W
1
mv2 W = Fd P =
.
2
t
Assessment Specifications for this achievement standard can be accessed
through the Science Resources page found at
www.nzqa.govt.nz/ncea/resources.
WSC 2013
Mechanics Revision
Key Words
Speed
Gravitational Potential Energy
Newton
Velocity
Pressure
Weight Force
Distance
Area
Mass
Acceleration
Pascal
Force
Power
Gravitational Force Field
Work
Kinetic Energy
Joules
Key Definitions
Speed
Acceleration
Pressure
Force
Work
Kinetic Energy
Gravitational
Potential Energy
Weight
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Revision – ESA Study Guide
AS90940:
Demonstrate understanding of aspects of mechanics
Chapter Title
Pages
Exercises
147 – 160
10A, 10B, 10C and
10D
11 Forces
161 - 176
11A. 11B. 11C and
11D
12 Energy, work and
power
177 - 194
12A, 12B, 12C, 12D
12E and 12F
10 Motion
(in a straight line)
Note: In this unit of work you will be required to calculate numerical answers.
Therefore, you will need a calculator in an assessment situation (you will not be
allowed to use a phone as a calculator).
When constructing your answers to questions, It is essential that you:
1. First write down the formula equation is you will be using.
2. Then substitute the data into the mathematical formula.
3. Write down your final answer when the calculation has been completed.
Correct units will be required in your final answer (either in symbols or words)
and all final answers will need to be rounded to an appropriate number of
significant figures (normally 3), but check the number of significant figures of
the data first.
If you are required in a question to explain a concept look at the information given
within a question to find examples which you can use to support your explanation. In
your answer use this information.
If a question asks you to explain or comment on a relationship between two
quantities (e.g. what will happen to Ek if velocity is doubled, Ek = ½mv2) try to show
what happens mathematically as well as explaining the concept in words.
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Mechanics Questions – CSTA 2011
You will find the following formulae useful.
v
d
t
a
EK 
1 2
mv
2
v
t
Fnet  ma
W  Fd
P
F
A
g  10 N kg 1
E p  mgh
P
W
t
QUESTION ONE: AEROPLANE WHEELS
A skydiving plane sits on the grass at the airport. The plane is sitting on three wheels, each
wheel has an area of 0.04 m2 in contact with the ground. When the plane is empty, it has a
weight of 15000 N.
a)
Calculate the mass of the empty plane. Give an appropriate unit with your answer.
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b)
Calculate the pressure of the tyres on the ground. Give an appropriate unit with your
answer.
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c)
The plane is then loaded up with fuel, equipment and passengers. This adds more
weight to the plane. The pressure of the wheels on the ground stays approximately
the same. Explain what weight is and explain what will happen to the area of the
wheels in contact with the ground as the plane is loaded up.
In your answer you should,
 define weight using words and an equation
 define pressure using words and an equation
 use your definition of pressure to explain what happens to the wheels.
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QUESTION TWO: TAKE OFF
The speed-time graph of the plane taking off is shown below.
Section A
Section B
Section C
In section A the plane is on the runway, preparing to take off.
In section B the plane is in the air and gaining height.
In section C the plane is flying level.
a)
Describe the motion of the plane during the first 200 seconds.
In your answer you should include values of the speeds and accelerations for
sections A, B and C. Show all your working and include units with your values.
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b)
Calculate the distance the plane travels in section B (as the plane is gaining height).
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c)
In section A of the previous graph, the plane is on the flat runway and the wings are
not producing any lift force. In section C of the graph, the plane’s wings are creating a
lift force and the plane is flying level. Discuss the forces on the plane during section
A and C of the plane’s motion.
In your answer you should:




Draw a labeled force diagram for each of section A and C.
State whether the forces are balanced or unbalanced for each section.
Describe the relative sizes of these forces for each section.
Explain how these forces cause the motion shown on the graph.
Force diagram for section A
Force diagram for section C
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QUESTION THREE: ENERGY AND POWER OF THE PLANE
At another part of the flight, the plane needs to gain height to climb over the mountains. At
this time the plane has a mass of 2100 kg. The plane moves at a constant speed of 70
m s-1 as it climbs in the air. During this time the upwards force on the plane is 21000 N. The
plane gains in altitude by 2200 m. The total distance the plane travels in this time is 6300 m.
It takes the plane 90 seconds to gain this height.
`
6300 m
2200 m
a)
Calculate the gravitational potential energy gained by the plane as the plane rises in
the air. Give an appropriate unit for your answer.
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b)
Discuss the types of energies and the energy transformations occurring as the plane
gains height while it is moving at this constant speed. In your answer you should
 State the value of the change in kinetic energy of the plane
 State the value of the change in potential energy of the plane
 Explain why the energy gained by the plane is much less than the
chemical energy used by the plane’s fuel.
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When the plane has climbed above the height of the mountains in level flight, the plane
accelerates from 70 ms-1, until it is moving at 85 ms-1. It takes 60 seconds for the plane to
speed up.
c)
Calculate the power of the aircraft as it is speeding up. Write an appropriate unit with
your answer. You should begin by calculating kinetic energies.
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QUESTION FOUR: SKYDIVING
An 80 kg skydiver jumps out of the plane. He deploys his parachute after he has fallen 1500
m.
a)
At the moment the skydiver jumps out of the plane he is not moving up or down, but
he begins accelerating. His gravitational potential energy is being turned into kinetic
energy. Calculate the speed of the skydiver when he deploys his parachute. Write
an appropriate unit with your answer.
Assume ALL his gravitational potential energy is turned into kinetic energy.
To answer this question you should begin by calculating the gravitational potential
energy the skydiver has before in his 1500 m fall.
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In reality, the skydiver’s gravitational potential energy does not ALL turn into kinetic energy.
When the skydiver first jumps out of the plane he accelerates at 10 m s-2. However, this
acceleration gets smaller and smaller until he reaches a constant speed called his terminal
velocity.
b)
Explain why the skydiver doesn’t continue accelerating at 10 m s-2, and why he
reaches a constant speed. In your answer, you should:
 Describe the forces acting on the skydiver, and explain how they change as
he falls.
 Explain how the forces create the observed motion.
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c)
When the skydiver (mass 80 kg) does deploy his parachute he slows down from 55
m s-1 to 10 m s-1 over 12 s. Calculate the average net force during this time. Give an
appropriate unit for your answer.
Start your answer by calculating the average deceleration of the skydiver.
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Mechanics Questions – CSTA 2012
QUESTION ONE: DRIVING TO THE CAVE
Jim and Bob are going caving. They drive the 50km (50 000m) to the cave in their car.
Distance - Time graph for the journey to the cave
60000
Distance (metres)
50000
40000
30000
20000
10000
0
0
500
1000
1500
2000
Time (seconds)
2500
3000
3500
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(a)
Use the distance – time graph to calculate the average velocity of the car. Give the
answer in meters per second.
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(b)
The car, with Jim and Bob inside, has a mass of 1500 kg. When they leave town they
accelerate away from the 50km/h zone. Initially they are travelling at 13.8 ms-1 and 30
seconds later reach a top speed of 27.7 ms-1. Calculate the Net Force acting on the
car. Give an appropriate unit with your answer.
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(c)
The net force making the car accelerate is not the only force on the car.
 Discuss all the forces acting on the car,
 Whether the forces are balanced or unbalanced
 How the forces affect the movement of the car
 How they change as the car accelerates and reaches a constant maximum
speed.
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QUESTION TWO: ABSEILLING INTO THE CAVE
Jim and Bob have to abseil down in to the cave. The section of the cave they abseil down is
47m high.
(a)
Jim has a mass of 85kg. Calculate the difference in Jim’s
potential energy between the top and bottom of the abseil. Give
an appropriate unit with your answer.
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(b)
Jim attempts to abseil down as rapidly as possible.



Discuss the assumptions made to be able to calculate the maximum velocity.
Calculate the maximum velocity Jim could achieve when he abseils down the
rope.
Discuss why it would not be possible for Jim to actually reach this maximum
velocity, and why he should not attempt to reach this velocity.
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QUESTION THREE: CLIMBING THE LADDER
To get back out of the cave, the cavers have to climb back up a ladder.
The ladder is 32m high. Jim, who has a mass of 85kg, finds it harder to
climb the ladder than Bob, who has a mass of 75kg. Jim is able to climb
the ladder in 7 minutes (420 seconds), while Bob takes 5 minutes (300
seconds).
http://www.pinnerchalkmine.info/3.html
(a)


Calculate the energy used by each climber when they climb the ladder, giving an
appropriate unit with your answer. You will need to calculate other quantities first.
Discuss how the amount of energy required would change if they each took twice
as long to climb the ladder.
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(b)
The cavers need to use energy to climb the ladder.
 Discuss the main energy transformations that take place while a caver is
climbing the ladder.
 Explain why the actual amount of energy required to climb the ladder will be
greater than what you calculated in (a) above.
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QUESTION FOUR: MUD GLORIOUS MUD
Jim and Bob have to walk across a section of mud. The mud can
withstand a pressure of 12,000 Nm-2 before the person sinks in.
For every 100 Nm-2 above 12,000 Nm-2 the person sinks in 1 cm.
Jim has a mass of 85kg and his shoes have an area of 0.070m2,
Bob has a mass of 75kg and his shoes have an area of 0.058m2.
Jim and Bob have a discussion about who will sink in the most. Jim decides because he has
the bigger mass he will sink in further.

Use calculations to show if the cavers will sink in to the mud and if so by how
much.
 Discuss the accuracy of Jim’s prediction. In your answer explain how force and area
interact to cause pressure.
Give appropriate units with all answers.
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