L 90940

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NEW ZEALAND QUALIFICATIONS AUTHORITY MANA TOHU MATAUR.ANGA 0 AOTEAROA

Level 1 Science, 2014

SUPERVISOR'S USE ONLY

90940 Demonstrate understanding of aspects of mechanics

Achievement

9.30 am Monday 10 November 2014 Credits: Four

Achievement with Merit Achievement with Excellence

Demonstrate understanding of aspects Demonstrate in-depth understanding of Demonstrate comprehensive of mechanics. aspects of mechanics. understanding of aspects of mechanics.

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.

If you need more space for any answer, use the page(s) provided at the back of this booklet and clearly number the question.

Check that this booklet has pages 2-16 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.

TOTAL

©New Zealand Qualifications Authority, 2014. All rights reserved.

Low Excellence

26 ASSESSOR' S USE ONLY

No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.

You may fi nd the fo llowing formulae useful.

!1d v= -

!1t

!1v a=-

M F = ma

net

2

P=F A

1 E = -rnv2

k 2 W=Fd g= ION kg-1 P= w t

QUESTION ONE: CYCLING

A cyclist and bike have a combined mass of 99 kg.

(a) Show that the combined weight is 990 N.

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00)( to -~ 0qo N O~j-et:t , tr.-ei~~ -i ~~ -t~ ~ra tritlltfl~! f'r{e

a.ci':J -o 1\ ~--c-~~ L t-

(b) The cyclist 's journey was plotted on the distance/ time graph below.

distance (m)

(i) Describe the motion of the cyclist in each of sections A, B, C, and D.

No calculations are required.

Section A: [ ~ C j' /;)t iS .Qll el<rat i 'j ~for 5 Se<oAJJ

Section B: l" ~ _ c ~r It~ -~ -~ ) fo r S 5~~0/\~j _

Science 90940, 2014

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Section C: _14 CJ~LiJ t 1)

) ( i Q-1tlJ --

Section D: } ~ _ ~jd_t_.s f _ I )

I\A6Vrtl ~l'\ ' --"-;:}!- ~~------ ---

3

) It! {f!<VIi) f" r 4~\eco•JJ ,...

(ii) Calculate the cyclist's speed during Section B.

v - IJ A - J.E... - 2 5 -I --- A-=c- -- 5 - M ------ --- ----- -----------

----------------------------------- - ---- ------

(c) A bike with a mass of20 kg is lifted onto a shelf that is 1.5 metres high. It takes 3 seconds to lift the bike.

Calculate the power required to lift the bike onto the shelf.

Before you calculate the power, you will need to:

• determine the weight force of the bike

• calculate the work done in lifting the bike.

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-----------------------

-----------

----------- ----

------ ------------ -- - --------------- ---------- ---- ---- --- ---- --------

------------------------------ - ----------- ---- - -

-- ----------------- ----- -------- -- - ---- -

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(d) A person pushed the same bike up a ramp so that it was also at a height of 1.5 m. It took them a longer time to do this than lifting the bike in part (c).

--· .... .. .. .. _________________ __ t ____ _ ... I

1.5 m

~-- ----------- --- --------- ------- _____________ ____ _________ j ____ _ Explain whether the power needed to push the bike up the ramp is more or less than when it is lifted straight up to the same height.

In your answer you should refer to force and energy.

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------0 --OOo _____ ---~-~---- -- -----0 --- 0-·-- -·-

---0 oo-oo ____ ---------··- -·-------0---- - -----

------0 --00 ___ 0 - --0- --0-

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5

QUESTION TWO: FURNITURE

A chair (15.0 kg) and footstool (15.0 kg) are shown below.

The chair has four legs in contact with the floor, whereas the base of the footstool does not have legs and is entirely in contact with the floor.

For copyright reasons, this image has not been

reproduced here.

http://st.houzz.com/simgs/e0217bad0e26c829 _ 4·5482/modem-aimchairs.jpg

(a) It took 6 seconds to push the footstool a distance of 8.0 m across a room.

Calculate the average speed of the footstool as it is pushed.

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(b) The footstool was pushed around the house.

Select the correct statement below and then explain your choice.

A. It is easier to push the footstool across carpet than across ·a wooden floor.

B. It is easier to push the footstool across a wooden floor than across carpet.

Write the letter of the correct statement: [ID Explain why you have selected this statement.

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(c) The area of each chair leg in contact with the floor is 0.001 m2.

Calculate the pressure that the chair (mass 15.0 kg) exerts on the carpet.

In your answer you must determine:

• the area of the chair legs in contact with the floor

• the weight force of the chair

• the pressure acting on the carpet.

(d) A person sat on the chair and then sat on the footstool for the same period of time. They noticed that the chair legs left deeper marks in the carpet than the footstool did, although both the chair and footstool have the same mass.

For copyright reasons, this image has not been

reproduced here.

-chair leg

_ mar.k left by chair leg

Explain these differences in terms of pressure, force, and surface area.

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-

8

QUESTION THREE: CONSTRUCTION

During the construction of a building, a long beam was lifted into place using a crane.

For copyright reasons, this image has not been

reproduced here.

http://www.countyofplumas.com/images/pages/N632//lifl ing%20beam.jpg

(a) Calculate the work done in lifting the beam with a weight of 6000 N through a distance of

50 m. \

lJ:. F d :: 6 00 0 X 5 0 - < '3 0 ~ 0 0 () J

(b) Explain why there is no work being done when the beam is banging in the air without moving.

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Science 90940, 2014

ASSESSOR"S USE ONLY

(c) Another crane was lifting wood. The cable broke, and 150 kg of wood fell 12 m to the ground below.

The wood had 15 000 J of kinetic energy just before it landed on the ground below.

This was different from the amount of energy the wood had when it was hanging from the crane.

Explain why there is a difference in the energy the wood had when it was hanging from the crane compared to just before it hit the ground.

In your answer you should:

• name the type of energy the wood

9

For copyright reasons, this image has not been

reproduced here.

http://theagregator.com/wp-conlent/uploads/2013/09/crane I .jpg

had when it was hanging from the crane ·

• calculate how much energy the wood had when it was hanging from the crane

• calculate the difference between the kinetic energy of the wood just before hitting the ground and the energy the wood had when it was hanging from the crane

• justify the difference in energy of the wood when it was hanging from the crane and then just before it hit the ground.

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--------

Science 90940, 2014

There is more space for your answer to this question on the following page.

ASSESSOR'S USE ONLY

10

Science 90940, 2014

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'\ \

'\ ,....-------------,

This page has been deliberately left blank.

e examination continues on the following page.

\ '

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QUESTION FOUR: GO-CART RACING

Two go-carts were racing on a track.

For copyright reasons, this image has not been

reproduced here.

http://static2.stutf.co.nz/13 77664598/017/9098017 .jpg

A speed/time graph is shown below for each go-cart. Zane's graph is shown in blue, and Francis's in red.

speed (m s-1)

20

18

16

\5 14

12

10

8

6

4

2

Section A~ :=J: ~ction B - F 1 =rsection C f--f+ ::..:: -:_--- - ... -=_-: ..:. - - -- - -_.:.------ -~--=- --:: -:..:- - -- -- _.,. ~

---+- --- -·---· ·+ ---t ~-= ·.::__j.:. -- .. ! ...-t -

. r-·--t·· -· ------- + ...

j ·- I ·- · ~- r./--'- --+-J - +-+ ··-. --· ...__ !--

---+-·---+- --~ _'" ____

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-=-t ----If--- ··- ----,- ······--f-- 1-- - - ·- -··-

-~= --f---· t -- 1- .. --f- f--- l _ ___ ... _ --,- --1--- ----- -H -- ~ -

g ... f-·- .. ---- v~ ;- -· !-

___ _J_ 1----- ---+-1-- ··- ·-- -- .... _. i·---·

- r · --- -----T 1·---· --· 1- •---'r

11 --------·-+-·--- ·-·-1-·

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t - - f-··

= -} -~ i ~-- 1- -- I· ... 1·-

--f- ---

• Zane

• Francis

r 0 0 '2. ' 4 5

i-10

time (s) 15

(a) Calculate the acceleration of Zane in the fi rst 3 seconds. - fjV- 2.2._ - 5 ~- 4t - ~ - !"\ s-1..

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13

(b) (i) On the photo below, draw and label ALL the forces acting on Zane's go-cart in Section B of the graph. The track is flat and horizontal. ·,

Ensure that your labels show the relative sizes of the forces.

<--

~ Su yport _

For copyright reasons,

n V frJi!frMI '!ff ll'ffC/) this image has not "' tJ been --?

reproduced here. w

w(7r~I11"/Qf''vl ij -www.kartsport.org.nzJimages/News/13<!oProKSNZNatsYamJnrMarcusArmstrong-l .jpg

(ii) Discuss the forces that are acting on Zane's go-cart to explain its motion in Section B of

'

the graph. · I

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act-e~ ~ t l\ ~ec frd l\ A. { C~==========~.....------1-

-

Science 90940, 2014

Question Four continues on the next page.

ASSESSOR'S USE ONLY

14

(c) Explain which go-cart travelled 200m around the track first.

In your answer you should:

• use the information in the graph

• show all working for the calculations

• compare the distances travelled by Zane and Francis by the end of 14 s.

Graph from page 12 speed (m s-1)

+ Zane

• Francis

time (s)

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2oo ~~.Aef-N J or-ov/\(1 ~ +-rar k frrs+, ( f ft,\All 5 ~t-ed ~ ·-; . S IV'{ f-lfs M ~ r'( .ft. CAl\ bvte , / -----,

--------------, -

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QUESTION NUMBER

16

Extra paper if required.

Write the question number(s) if applicable.

---------

----------------

-----·-·-·--

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Low excellence Exemplar (Total score: 26)

Question 1 (M6)

(a) Correctly showed the weight of 990N through calculation (b) (i) Correctly described the motion in two sections

(ii) Correctly calculated speed

(c) Correctly calculated Weight force, work and power

(d) Explained longer time resulted less power and recognised gaining same amount of gravitational energy. However, the suggestion of increased work was not backed up with correct reason led to merit at this part of the question

Question 2 (E8)

(a) Correctly calculated average speed

(b) Recognised there is more friction when pushing the stool across the carpet. Explained more energy needed to push across carpet due to the loss of energy caused by friction

(c) Correctly calculated weight, surface area (without unit) and pressure

(d) Clearly explained the relationship among pressure, surface area, and weight force between the chair and footstool and led to the conclusion of the sizes of the marks left on the carpet

Question 3 (M5)

(a) Correctly calculated work done

(b) Used formulae for work to explained why no work done when distance equals to zero

(c) Correctly named Gravitational potential energy when the wood was hanging from the crane. Calculated Gravitational potential energy and energy difference Recognised energy lost to heat and sound due to friction without discussion where friction (air resistance) from and how energy was transformed.

Question 4 (E7)

(a) Correctly calculated acceleration

(b) (i) Correctly named and labelled all the forces and with equal sizes (ii) Explained balanced forces with zero net force which resulted no acceleration (constant speed)

(c) Correctly calculated distances for each section for both racers and explain Francis winning the race by comparing the total distances travelled by t end of the 14 s.