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90255
2
902550
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Level 2 Physics, 2011
90255 Demonstrate understanding of mechanics
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November 2011
Credits: Six
Check that the National Student Number (NSN) on your admission slip is the same as the number at the
top of this page.
You should attempt ALL the questions in this booklet.
Make sure that you have Resource Sheet L2–PHYSR.
In your answers use clear numerical working, words and / or diagrams as required.
Numerical answers should be given with an appropriate SI unit.
If you need more room for any answer, use the extra space provided at the back of this booklet.
Check that this booklet has pages 2 – 10 in the correct order and that none of these pages is blank.
YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.
ASSESSOR’S USE ONLY
Achievement
Achievement Criteria
Achievement with Merit
Achievement with Excellence
Identify or describe aspects
of phenomena, concepts or
principles.
Give descriptions or explanations
in terms of phenomena,
concepts, principles and / or
relationships.
Give concise explanations that
show clear understanding in
terms of phenomena, concepts,
principles and / or relationships.
Solve straightforward problems.
Solve problems.
Solve complex problems.
Overall level of performance
© New Zealand Qualifications Authority, 2011. All rights reserved.
No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.
2
You are advised to spend 60 minutes answering the questions in this booklet.
ASSESSOR’S
USE ONLY
All formulae are provided on the separate Resource Sheet L2-PHYSR.
QUESTION ONE: THE BIKE RIDE
(a)
Jacquie is a bike rider. One morning she starts riding from rest and
accelerates at 1.2 m s–2 for 14 seconds.
Show that her final velocity after 14 seconds is 16.8 m s–1.
(b) She heads East at a constant speed of 16.8 m s–1, then turns left (heads
North), without changing speed.
Draw a vector diagram and use it calculate the change in her velocity
(size and direction).
N
W
E
S
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(c)
Jacquie takes her bike on a boat across a river 65 m wide. The boat heads straight across (↑)
the river, with a speed of 6.8 m s–1 relative to the water. The current (→) causes the boat to
land 15 m downstream.
Calculate the speed of the boat relative to the bank (ground).
You may begin your answer by drawing labelled vector diagrams for distances and speeds.
(d) Jacquie then rides along a horizontal circular path at constant speed.
Describe what it is that provides the force needed to keep the bike going in a circle.
State the direction of this force.
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QUESTION TWO: THE BRIDGE
ASSESSOR’S
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Jacquie cycles along a uniform bridge that is supported at both ends, as shown in the diagram.
25.0 m
5.0 m
A
B
(a)
The length of the bridge is 25.0 m. The mass of Jacquie and her bike is 72 kg. The mass of the
bridge is 760 kg. Calculate the support force (FA) provided by end A and the support force (FB) provided by
end B of the bridge when Jacquie is 5.0 m from end A.
(b) Express your answers to part (a) to the correct number of significant figures.
Give a reason for your choice of significant figures in your answers to part (a).
(c)
While Jacquie is cycling at a speed of 16.8 m s–1, she collides with a soccer ball that is rolling
towards her at a speed of 8.0 m s–1. The soccer ball bounces off in the opposite direction with
a speed of 5.0 m s–1.
16.8 m s–1
8.0 m s–1
5.0 m s–1
before collision
after collision
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Calculate Jacquie’s velocity (size and direction) after the collision.
You may ignore any effects of friction.
Mass of Jacquie and her bike = 72.0 kg
Mass of soccer ball = 0.430 kg.
(d) Explain what is meant by an elastic collision and an inelastic collision.
Elastic collision:
Inelastic collision:
Describe what you would need to do in order to determine whether this collision between the
bike and the soccer ball is elastic or inelastic.
You are not required to carry out any calculations.
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(e)
Explain how the force exerted by the ball on Jacquie and her bike is dependent on the duration
of the time on impact, AND explain how the force exerted by the ball on Jacquie and her bike
is related to the force exerted by Jacquie and her bike on the ball.
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QUESTION THREE: ENERGY AND PROJECTILE MOTION
Jacquie’s brother Ernie is pushing a lawn mower with a force of 26 N at an angle of 34° to the
ground, as shown below.
For copyright reasons, this resource
cannot be reproduced here.
www.treehugger.com/push-mower-jjh01.jpg
(a)
Explain fully why not all of the 26 N force exerted by Ernie is used to push the lawn mower
horizontally along the ground.
(b) Calculate the power produced by Ernie when he accelerates the mower through a distance of
4.0 m in 3.0 seconds.
Give the correct units for your answer.
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(c)
Ernie’s son Jacob kicks a ball towards Ernie in the garden. Ernie is 1.75 m tall. Jacob kicks
the ball with a velocity of 24 m s–1 at an angle of 36° to the ground. Jacob is standing 35 m
away from Ernie.
Ernie
Diagram is
NOT to scale
Jacob
1.75 m
24 m s–1
36°
35 m
Will the ball hit Ernie or go over his head?
In your calculations, start by showing that the horizontal component of the initial velocity of
the ball is 19.4 m s–1.
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9
A spider spins a web in the garden and a moth gets caught in the web.
The web stretches downwards by 0.065 m when the moth of mass 0.003 kg is caught in it.
A graph for force against extension for the spider’s web is shown below.
force (N)
extension (m)
(d) Explain why the formula W = Fd cannot be used to calculate the elastic potential energy
stored in the web when the moth gets caught in it.
Your explanation should include a statement of what should be used to calculate this energy.
(e)
Calculate the elastic potential energy stored in the web when the moth is caught in the web.
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10
QUESTION
NUMBER
Extra space if required.
Write the question number(s) if applicable.
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90255