Chapter 2 Force and Motion STUDENTS MODULE

8/13/2019 Chapter 2 Force and Motion STUDENTS MODULE

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Physics Module Form 4

Chapter 2 : Force and Motion

2. FORCE AND MOTION

2.1 ANALYSING LINEAR MOTION

Distance and displacement

1. Types of physical quantity:

(i) Scalar quantity: .

(ii) Vector quantity:

2. The difference between distance and displacement:

(i) istance:

(ii) isplacement:

!. istance always lon"er than displacement.

#. $%ample: The followin" dia"ram shows the location of &ohor 'ahru and esaru.

ou can trael by car usin" e%istin" road ia *ota Tin""i+ or trael by asmall plane alon" strai"ht path.

,alculate how far it is from &ohor 'ahru to esaru if you traeled by:a. The car

b. The plane

Solution:

-andson /ctiity 2.2 p" 10 of the practical boo.dea of distance and displacement+ speed and elocity.

Speed and velocity

1. Speed is ..

2. Velocity is: .....

!. /era"e of speed:

#. /era"e of elocity: ...

1

*ota Tin""i

30 m

#1 m 4! m

esaru&ohor 'ahru


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4. $%ample:

/n aeroplane flies from / to '+ which is located !00 m east of /. 5pon reachin" '+ theaeroplane then flies to ,+ which is located #00 m north. The total time of fli"ht is #

hours. ,alculate

i. The speed of the aeroplane

ii. The elocity of the aeroplane

Solution:

Acceleration and deceleration

1. Study the phenomenon below6

7bseration:

2. /cceleration is+ .

Then+ a 8

!. $%ample of acceleration6

2

20 m s10 m s1

#0 m s1

Or, a v u

t

20 m s10 m s1 #0 m s1

/ ' ,

t 8 2 s t 8 2 s


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,alculate the acceleration of car6

i) from / to '

ii) 9rom ' to ,

#. eceleration happens ...

4. $%ample of deceleration6

/ lorry is moin" at !0 m s1+ when suddenly the drier steps on the braes and it stop 4seconds later. ,alculate the deceleration of lorry.

Analysing o motion

1. inear motion can be studied in the laboratory usin" a ticer timer and a ticer tape.

;efer te%t boo photo picture 2.# pa"e 23.

(i) etermination of time:

(ii) etermination of displacement as the len"th of ticer tape oer a period of time.

%

y

(iii) etermine the type of motion6

..

......

!

20 0 2= 10 m s-2

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .


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...

(i) etermination of elocity

displacement 8 time 8 ..

Velocity+ 8

() etermine the acceleration

T!e e"#ation o motion

1. The important symbols : ..

2. The list of important formula6

!. $%ample 1 : / car traelin" with a elocity of 10 m s1accelerates uniformly at a rate of !

m s2for 20 s. ,alculate the displacement of the car while it is acceleratin".

#

en"th

3

4

#

!

2

1

0

u

tics

. . . . . . . .


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$%ample 2 : / an that is traelin" with elocity 13 m s1decelerates until it comes to rest.f the distance traeled is = m+ calculate the deceleration of the an.

E$ecise 2.%

1. 9i"ure 2.1 shows a tape chartconsistin" of 4tic strip. escribe

the motion represented by /' and ',.

n each case+ determine the 6

(a) displacement

(b) aera"e elocity

9i"ure 2.1

(c) acceleration

2. / car moin" with constant elocity of #0 ms1. The drier saw and obtacle in front andhe immediately stepped on the brae pedal and mana"ed to stop the car in = s. The

distance of the obstacle from the car when the drier spotted it was 1=0 m. -ow far is the

obstacles from the car has sttoped.

4

en"th < cm

13

12

=

#

0/ ' , Time


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2.2 ANA&'SIN( MOTION (RA)*S

The data of the motion of the car can be presented.

T!e displacement+time (rap!

3

0m 100m 200m !00m #00m 400m displacement

0s 10s 20s !0s #0s 40s time

a) displacement (m) ?raph analysis:

time (s) ...

b) displacement (m) ?raph analysis:

..

@

time (s) .

c) displacement (m) ?raph analysis:

.

time (s) ..

d) isplacement (m) ?raph analysis:

.

..

time (s)


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d) (m s1) ?raph analysis:

.......

..

t (s)

....

e) (m s1) ?raph analysis:

......

.

..

t (s)

E$amples

1. s


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E$cercise 2.2

1. (a) s


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2., -NDERSTANDIN( INERTIA

Idea o inertia

1.

2.

!.

-andon actiity 2.4 in pa"e 1= of the practical boo to "ain an idea of inertia

#. Deanin" of inertia :

...

Mass and inertia

1. ;efer to fi"ure 2.1# of the te%t boo+ the child and an adult are "ien a push to swin".

(i) which one of them will be more difficult to be moed ...

(ii) which one of them will be more difficult to stopE .

2. The relationship between mass and inertia : .

..

!. The lar"er mass .

Eects o inertia

1. Aositie effect :

(i)

(ii)

(iii)

2. Fe"atie effect : .

(i) ...

..

(ii)

10


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(iii)

(i)

E$ecise 2.,

1. Ghat is inertiaE oes 2 " roc hae twice the inertia of 1 " rocE

2.

9i"ure 2+!

/ wooden dowel is fitted in a hole throu"h a wooden bloc as shown in fi"ure 2.!1.$%plain what happen when we

(a) strie the top of the dowel with a hammer+

(b) hit the end of the dowel on the floor.

2. ANA&'SIN( MOMENT-M

Idea o moment#m

1. Ghen an obHect ic moin"+ ...

2. The amount of momentum ...

!. Domentum is defined.

11


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Conservation o moment#m

T!e principle o conservation o moment#m /

1. $lastic collision ...

12

(mbI m

")

mg

vg = 0

mb

vb&g

Startin" position beforeshe catches the ball

vb

Receiving a massive ball

mb

vb

m"

vg

Startin" position

before she throws

the ballThrowing a massive ball

m1m2 m1

m2

u2 2

u1


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'efore collision after collision

2. nelastic collision :...

'efore collision after collision

!. e%plosion : ........

'efore e%plosion after e%plosion

$%ample 1 :

,ar / ,ar '

,ar / of mass 100 " traelin" at !0 m s1collides with ,ar ' of mass C0 " traelin" at20 m s1in front of it. ,ar / and ' moe separately after collision. f ,ar / is still moin" at

24 m s1after collision+ determine the elocity of ,ar ' after collision.

Solution :

$%ample 2 :

,ar / of mass 100 " traelin" at !0 m s1collides with ,ar ' of mass C0 " traelin" at

20 m s1in front of it. ,ar / is pulled by ,ar ' after collision. etermine the common elocity of

,ar / and ' after collision.

1!

m1m2

m1I m2

u2 8 0

u1

(m1I m2)+ u 8 0 1

m2

2


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Solution :

$%ample ! :

/ bullet of mass 2 " is shot from a "un of mass 1 " with a elocity of 140 m s1. ,alculate the

elocity of the recoil of the "un after firin".

Solution :

E$ercise 2.

1. /n arrow of mass 140 " is shot into a wooden bloc of mass #40 " lyin" at rest on asmooth surface. /t the moment of impact+ the arrow is traellin" hori@ontally at 14 ms1.

,alculate the common elocity after the impact.

2. / riffle of mass 4.0 " fires a bullet of mass 40 " with a elocity of =0 m s1 .,alculate the

recoil elocity. $%plain why the recoil elocity of a riflle is much less than the elocity ofthe bullet.

2.0 -NDERSTANDIN( T*E EFFECT OF A FORCE

Idea o orce

1. Ghat will happen when force act to an obHectE

1#


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Idea o 1alanced orces

1. /n obHect is said to be in balance when it is:

2. Stationary obHect

e%planation :

...

!. /n obHect moin" with uniform elocity

.. e%planation :

... ..

..

..

...

..

..

Idea o #n1alanced orces

1. A body is said to be in unbalanced

2. .. $%planation6

..

Relations!ip 1eteen orces3 mass and acceleration 4F 5 ma6

14

Stationary obHect


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!"periment 22 page 2#

/im : To inesti"ate the relationship between acceleration and force applied on a constant

mass.

!"periment 2$ page $%

/im: To inesti"ate the relationship between mass and acceleration of an obHect underconstant force.

1. ;efer to the result of e%periment 2.2 and 2.!+

2. 1 newton (9 8 1 F) is defined as the force required to produce an acceleration of 1 m s2

(a81 m s2) when its actin" on an obHect of mass 1 " ( m 8 1 ")So+

!. $%ample 1 : ,alculate 9+ when a8 ! m s2dan m8 1000 "

$%ample 2 :

,alculate the acceleration+ aof an obHect.

E$ercise 2.0

1. / trolley of mass !0 " is pulled alon" the "round by hori@ontal force of 40 F. The

opposin" frictional force is 20 F. ,alculate the acceleration of the trolley.

13

m 8 24 "m 8 24 "

9 8 200 F9 8 200 F


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2. / 1000 " car is traellin" at >2 m h1when the braes are applied. t comes to a stop in

a distance of #0 m. Ghat is the aera"e brain" force of the carE

2.7 ANA&'SIN( IM)-&SE AND IM)-&SI8E FORCE

Imp#lse and imp#lsive orce

1. mpulse is .

2. mpulsie force is

!. 9ormula of impulse and impulsie force:;efer+ 9 8 ma

$%ample 16 u

wall

f 6 u 8 10 m s1+ 8 10 m s1+ m 8 4 " and t 8 1 s

mpulse+ 9t 8 and impulsie force+ 9 8

$%ample 26 u

Gall with a soft surface

1>


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f 6 u 8 10 m s1+ 8 10 m s1+ m 8 4 " and t 8 2 s

mpulse+ 9t 8 and impulsie force+ 9 8

#. The relationship between time of collision and impulsie force.

E$ercise 2.7

1. / force of 20 F is applied for 0.= s when a football player throws a ball from the sideline.

Ghat is the impulse "ien to the ballE

2. / stuntman in a moie Humps from a tall buildin" an falls toward the "round. / lar"e

canas ba" filled with air used to brea his fall. -ow is the impulsie force reducedE

2.9 :EIN( A;ARE OF T*E NEED FOR SAFET' FEAT-RES IN 8E*IC&ES

1=


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Importance o saety eat#res in ve!icles

Saety eat#res Importance

Aadded dashboard&ncreases the time interval o' collision so the impulsive 'orceproduced during an impact is thereby reduced

;ubber bumper Absorb impact in minor accidents( thus prevents damage to the car

Shatterproof windscreen Prevents the windscreen 'rom shattering

/ir ba"Acts as a cushion 'or the head and body in an accident and thusprevents in)uries to the driver and passengers

Safety seat beltPrevents the passengers 'rom being thrown out o' the car *lows

down the 'orward movement o' the passengers when the car stopsabruptly

Side bar in doors

Prevents the collapse o' the 'ront and bac+ o' the car into the

passenger compartment Also gives good protection 'rom a side,on

collision

E$ercise 2.9

1. 'y usin" physics concepts+ e%plain the midifications to the bus that help to improe thatsafety of passen"ers and will be more comfortable.

1C

Safety features in vehicles

Crash resistant doorpillars

Anti-lock brakesystem (ABS)

Traction control bumpers

indscreen

Air ba!s

"ead rest

Crumple #ones

$ein%orced passen!er compartment


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2.< -NDERSTANDIN( (RA8IT'

,arry out handson actiity 2.= on pa"e !4 of the practical boo.

Acceleration d#e to gravity.

1. /n obHect will fall to the surface of the earth because...

2. The force of "raity also nown ...

!. Ghen an obHect falls under the force of "raity only+ ...

#. The acceleration of obHects fallin" freely

4. The ma"nitude of the acceleration due to "raity depends ...

(ravitational ield

1. The re"ion around the earth is .

2. The obHect in "raitational field

!. The "raitational field stren"th is defined ..

#. The "raitational field stren"th+ " can be calculate as6

4. /t the surface of the earth+ .

..

3. This means

..

20


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>. $%ample 1. ,an you estimate the "raitational force act to your bodyE

mass 8 30 "+ " 8 C.= F "1+ 9 8 E

$%ample 2+

/ satellite of mass 300 " in orbit e%periences a "raitational force of #=00 F. ,alculatethe "raitational field stren"th.

$%ample !+/ stone is released from rest and falls into a well. /fter 1.2 s+ it hits the bottom of the

well.(a) Ghat is the elocity of the stone when it hits the bottomE

(b) ,alculate the depth of the well.

;eig!t

1. The wei"ht of an obHect is defined ..

2. 9or an obHect of mass m+ the wei"ht can be calculate as :

$%ample : The mass of a helicopter is 300 ". Ghat is the wei"ht of the helicopter

when it land on the pea of a mountain where the "raitational field isC.>= F "1E

21


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E$ercise 2.-I&I:RI-M FORCES

/n obHect is in e"#ili1ri#mwhen :

1.

2.

stationary obHect

22


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/n obHect moin" with uniform elocity

Addition o Force

1. /ddition of force is defined as .....

!"amples : the 'orces are acting in one direction

918 10 F

928 4 F

;esultant force+ 9

!"ample : the 'orces are acting in opposite directions

918 10 F

928 4 F

;esultant force+ 9

!"ample : the 'orces are acting in di''erent directions

928 4 F

400

2!


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918 10 F

Aarallelo"ram method:

1. raw to scale.

2. raw the line parallel with 91to the ed"e of 92+ and the line parallel with 92to the

ed"e of 91

!. ,onnect the dia"onal of the parallelo"ram startin" from the initial point.

#. Deasure the len"th of the dia"onal from the initial point as the alue of the

resultant force.

92

91

Trian"le method

1. raw to scale.

2. isplace one of the forces to the ed"e of another force.

!. ,omplete the trian"le and measure the resultant force from the initial

point.

$%ample 1: urin" Sport ay two teams in tu" of war competition pull with forces of

3000 F and 4!00 F respectiely. Ghat is the alue of the resultant forceE

/re the two team in equilibriumE

$%ample 2: / boat in a rier is pulled hori@ontally by two wormen. Gormen /

2#


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pulls with a force of 200 F while wormen while wormen ' pulls with a

force of !00 F. The ropes used mae an an"le 240with each other. raw a

parallelo"ram and label the resultant force usin" scale of 1 cm : 40 F.

etermine the ma"nitude of resultant force.

Resol#tion o a orce

1. ;esolution of a force is

;efer to tri"onometric formula:

$%ample : The fi"ure below shows /li moppin" the floor with a force 40 F

at an an"le of 300to the floor.

9 8 40 F

24


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$%ample of resolution and combination of forces

)ro1lem solving

1. Ghen a system is in equilibrium+ .

2. f all forces actin" at one point are resoled into hori@ontal and ertical

components+

!. $%ample 16 Show on a fi"ure6

a) the direction of tension force+ T of strin"

b) the resultant force act to lampc) calculate the ma"nitude of tension force+ T

a)

mlamp8 1.4 "

Glamp 8 1#.> F

E$ercise 2.=

1. Two force with ma"nitude 1= F and 3 F act alon" a strai"ht line. Gith the aid of

dia"rams+ determine the ma%imun possible alue and the minimum possible alue of the

resultant force.

23

F = ?

200 N

400

T b) TJ T

700 700


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2. / football is iced simultaneously by two players with force 220 F and 200 Frespectiely+ as shown in 9i"ure 2.C. ,alculate the ma"nitude of the resultant force.

220 F

C00

200 F

2.%? -NDERSTANDIN( ;OR@3 ENER(' AND EFFICIENC'

;or

1. Gor is done+ ..

2. G7;* is the product..

!. The formulae of wor6

#. $%ample 16

$%ample 26

2>

9orce+ 9

s


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=0 F

300

s 8 4 m

$%ample !6

98 !0 F h 8 1.4 m

$%ample #6

9 8 300 F

S 8 0.= m

Energy

1. $ner"y is .................................................................................................................

2. $ner"y cannot be ....................................................................................................

2=


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!. $%ist in arious forms such as ...

#. $%ample of the ener"y transformation6

4.

$%ample :

;or done and t!e c!ange in inetic energy

1. *inetic ener"y is

2. ;efer to the fi"ure aboe+

!. $%ample 16 / small car of mass 100 " is moin" alon" a flat road. The

resultant force on the car is 200 F.a) Ghat is its inetic ener"y of the car after moin" throu"h 10 mE

b) Ghat is its elocity after moin" throu"h 10 mE

2C

s

Force, F

Throu!h, v&' u&&asu '

and, as ' * v&


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;or done and gravitational potential energy

h 8 1.4 m

1. ?raitational potential ener"y is...

2.

;efer to the fi"ure aboe6

!. $%ample6 f m 8 10 "

)rinciple o conservation o energy

,arry out handson actiity 2.10 on pa"e != of the practical boo.

To show the principle of conseration of ener"y.

1. $ner"y cannot be

2. $%ample : a thrown ball upwards will achiee a ma%imum hei"ht before chan"in" its

direction and falls

!. $%ample in calculation : / coconut falls from a tree from a hei"ht of 20 m. Ghat is the

elocity of coconut Hust before hittin" the earthE

!0


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)oer

1. Aower is

2. / wei"htlifter lifts 1=0 " of wei"hts from the floor to a hei"ht of 2 m aboe his head in atime of 0.= s. Ghat is the power "enerated by the wei"htlifter durin" this timeE

" 8 C.= ms2)

Eiciency

1. efined...

2. 9ormulae of efficiency :

!. /nalo"y of efficiency6

$ner"y transformation

#. $%ample6 /n electric motor in a toy crane can lift a 0.12 " wei"ht throu"h a hei"ht of

0.# m in 4 s. urin" this time+ the batteries supply 0.= & of ener"y to the motor. ,alculate(a) The useful of output of the motor.

(b) The efficiency of the motor

!1

Device/

meci!e

Device/

meci!e


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,arry out handson actiity 2.11 on pa"e !C of the practical boo to measure the power.

E$ercise 2.%?

1. Ghat is the wor done by a man when he pushes a bo% with a force of C0 F throu"h a

distance of 10 mE State the amount of ener"y transferred from the man to the force.

2. / sales assistant at a shop transfers 40 tins of mil powder from the floor to the top shelf.

$ach tin has a mass of !.0 " and the hei"ht of thee top shelf is 1.4 m.

(a) ,alculate the total wor done by the sales assistant.

(b) Ghat is his power if he completes this wor in 240 sE

2.%% A))RECIATIN( T*E IM)ORTANCE OF MABIMISIN( T*E EFFICIENC'

OF DE8ICES

!2


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1. urin" the process of transformation the input ener"y to the useful output ener"y+

..

2. ...

!.

$%ample of wastin" the ener"y6

..

nput ene"y output

from the petrol ener"y

. .

.... .. .. .

.... . . .

#. The world we are liin" in face acute shorta"e of ener"y.

4. t is ery important that a deice maes

;ays o increasing t!e eiciency o devices

1. -eat en"ines ..

2. $lectrical deices. ......

!!


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Operation o electrical devices

1. The electrical deices increase the efficiency.

2. Aroper mana"ement .....

!. ..

2.%2 -NDERSTANDIN( E&ASTICIT'

,arry out -andson actiity 2.12 pa"e #0 of the practical boo.

1. $lasticity is ...

2. 9orces between atoms ..

!. 9orces between atoms in equilibrium condition

$%planation :

#. 9orces between atoms in compression

!#

Force o" re#$%sio!

Force o" ''rc'io!

Force o" re#$%sio!

compressie forcecompressie force

9orce of repulsion9orce of repulsion


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$%planation 6

4. 9orces between atoms in tension

force of attraction

stretchin" force stretchin" force

$%planation 6

,arry out $%periment 2.# on pa"e #1 of the practical boo

To inesti"ate the relationship between force and e%tension of a sprin"

*ooes &a

1. -ooeJs aw states

2. $lastic limit of a sprin" is defined.

!. The sprin" is said to hae a permanent e%tension+...

#. The elastic limit is not e%ceeded+.

4. ?raf 9 a"ainst %?raf 9 a"ainst %

9< F

!4

( )cm*0

+Q

P

R


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3. Sprin" ,onstant+

9


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Elastic potential energy

1. $lastic potential ener"y ..

sprin" with the ori"inal len"th

9 compression

% sprin" compressed %

9 % 8 compression %

% 9 sprin" e%tended

% 8 e%tension 9+ e%tension

7ther situation where the sprin" e%tendedand compressed

Relations!ip 1eteen or and elastic potential energy

?raph 9 a"ainst %

$%ample 6

Factors t!at eect elasticity

-andson actiity 2.1! on pa"e #2 the practical boo to inesti"ate the factors that affectelasticity.

Type of material different same same same

iameter of sprin" wire same different same same

iameter of sprin" same same different same

!>

( / cm

F/N

F (

1. cm

. g

cm


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en"th of sprin" same Same same different

Summarise the four factors that affect elasticity

9actor ,han"e in factor $ffect on elasticity

en"thShorter sprin" ess elastic

on"er sprin" Dore elastic

iameter of sprin"Smaller diameter ess elastic

ar"er diameter Dore elastic

iameter of sprin" wireSmaller diameter Dore elastic

ar"er diameter ess elastic

Type of material the elasticity chan"es with the type of materials

E$ercise 2.%2

1. / 3 F force on a sprin" produces an e%tension of 2 cm. Ghat is the e%tension when the

force is increased to 1= FE State any assumption you made in calculatin" your answer.

2. f a 20 F force e%tends a sprin" from 4 cm to C cm+

(a) what is the force constant of the sprin"E

(b) ,alculate the elastic potential ener"y stored in the sprin".

Reinorcement C!apter 2

)art A / O1ective >#estions

1. Ghen a coconut is fallin" to the"round+ which of the followin"

quantities is constantE

/. Velocity

'. Domentum

,. /cceleration

. *inetic ener"y

!=


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2. n an inelastic collision+ which of the

followin" quantities remains

constant before and after thecollisionE

/. Total acceleration '. Total elocity

,. Total momentum

. Total inetic ener"y!. ,alculate the wei"ht of a stone with

mass 30 " on the surface of the

moon.

(The "raitational acceleration of themoon is 1. This fi"ure shows an aircraft flyin"

in the air.

=. m 8 0.! "

4 m

Ghat is the momentum of the stone

Hust before it hits the "roundE

/. 0.14 " m s1

'. 0.! " m s1

,. 1.4 " m s1. !.0 " m s1

$. 14.0 " m s1

Solution :

!C

ift

Thrust /ir friction

Gei"ht

The aircraft aboe accelerates if

/. ift >Gei"ht

'. Thrust >ift

,. ift >/ir friction

. Thrust >/ir friction


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C. / bi" ship will eep moin" for some distance when its en"ine is turned off.

This situation happens because the ship

has

/. "reat inertia

'. "reat acceleration

,. "reat momentum. "reat inetic ener"y

10. /n iron ball is dropped at a hei"ht of10 m from the surface of the moon.

,alculate the time needed for the

iron ball to land.

(?raitational acceleration of themoon is 1


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(iii) acceleration of the car in method '.

( c ) Su""est a method to moe ,ar ' so that the acceleration produced is equal to that

of method /.

..

..

2. ceilin"

Tin water D F hand

A B ;(i) ia"ram 2.1 (ii)

a) ia"ram 2.1(i) shows tin A that is empty and tin B that is filled with water. /

student find difficult to pushed tin B. Grite the inference about the obseration.

b) ia"ram 2.1(ii) shows a tin bein" released from the different positions D and F.The hand of a student at position ; needs "reater force to stop the motion of the

tin fallin" from position D. $%plain this obseration.

c) 'ased on the obseration (i) and (ii)+ state two factors that affect the ma"nitude ofthe momentum of the obHect.

d) f water flows out from a hole at the bottom of the tin B+ how would the inertia ofTin B depends on time E

!. 2 ms1

A iron ball ( 2 " )

#1


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S T

!.0 m smooth surface

1.0 m 2.0 m

B ;

ia"ram ! ;ou"h surfaceThe fi"ure shows a iron ball that is rolled throu"h AB;ST. The rou"h surface of B; has

frictional force of # F.

a) ,alculate(i) the inetic ener"y of the iron ball at A.

(ii) the potential ener"y of the iron ball at A.

(iii) the total of ener"y of the iron ball at A.

b)

c) (i) ,alculate the total of ener"y of the iron ball when it reaches at B E

(ii) ,alculate the wor done a"ainst friction alon" B;.

d) ,alculate the total inetic ener"y of the iron ball at S.

e) ,alculate the speed of the ball at position T.

)art C / Essay >#estions

1.

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(i) (ii)

ia"ram 1.1ia"ram 1.1(i) shows the condition of a car moin" at hi"h elocity when it suddenly

crashes into a wall.

ia"ram 1.1(ii) shows a tennis ball hit with racquet by a player.a) (i) Ghat is the meanin" of momentumE

(ii) 'ased on the obserations of ia"ram (i) and (ii)+ compare the

characteristics of car when it crashes into the wall and the tennis ball whenit is hit with a racquet. -ence+ relate these characteristics to clarify a

physics concept+ and name this concept.

b) $%plain why a tennis player uses a taut racquet when playin".

c) n launchin" a rocet+ a few technical problems hae to be oercome before the

rocet can moe upri"ht to the sy. 'y usin" appropriate physics concepts+describe the desi"n of a rocet and the launch techniques that can launch the

rocet upri"ht.

Answera- .i- momentum is product o' mass and velocity

.ii- , The shape o' car changed but the shape o' wall remained, The shape o' ball remained but the shape o' the rac/uet string was

changed .The rac/uet string is elastic but the wall is harder-

, The time ta+en o' collision between the ball and rac/uet string morethan

the time ta+en when the car hit the wall

, The impulsive 'orce will decrease when the time o' collision increased, The concept is the impulsive 'orce

b- , To decrease the time o' collision between the ball and the rac/uet string

, &mpulsive 'orce will be increased, The 'orce act to the ball will be increased

, The velocity o' ball will be increased

c- , Ma+e a gradually narrower at the 'ront shape .tapering-

: To decrease air 'riction

, Made by the high strength and high rigidity o' materials: To decrease the probability to become dented .+emi+-

, Made by the low density o' material

: To reduce the mass0weight

, The structure is 'ractional engine

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: The mass will be decreased and the velocity will increase

, Made by the high o' heat capacity o' materials

: &t will be high heat resistance

2. 'rand ;eaction time < s Dass < "

$n"ine thrust

force < F

;esistance

force < F

/ 0.! 1.4 10.0 #.0

' 0.4 1.= 12.4 2.#

, 0.2 0.C 3.4 2.2

0.3 2.4 13.0 3.4

n a radiocontrolled car racin" competition+ # minicars branded /+ '+ , and toopart. The information of the # cars is "ien in the table aboe. etails of the aboe

information are "ien as below6

;eaction time uration between the moment the radiocontrolled is switched on and the moment the car starts moin".

;esistance /era"e alue of opposin" forces includes the friction between

wheels and trac+ and air resistance.

(a) Ghat is the meanin" of accelerationE

(b) raw a "raph of elocity a"ainst time that shows a car moin" initially withconstant acceleration+ then moin" with constant elocity and followed by

constant deceleration until it stops.

(c) $%plain the suitability of the properties in the aboe table in constructin" a radio

controlled car racin" purpose. -ence+ determine which brand of car will win the

40metre race.

(c) f ,ar ' in the aboe table is moed up the plane at the an"le of !0o to the

hori@on+

(i) Show that the car is able to moe up the plane.(ii) etermine the acceleration of the car.

Aroperties

Chapter 2 Force and Motion STUDENTS MODULE

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