linear motion.docx

8/10/2019 Linear Motion.docx

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iii. /dditional equipment- starting bloc* (reason- increaseforward force at starting)

0. /n object is under going a deceleration when it is slowing down. ,he rate of change of velocity of the object has a negative value.

. ,he tic*er time can be used to measure the velocity andacceleration of an object.

. ,he tic*er timer uses an a.c. $345 power supply. ,herefore

i. Ma*es $3 tic*s on the tic*er tape in one second.

ii. Ma*es one tic* in 3.32 second. PH#14

b.


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c. /n object which start to move with an initial velocity# u and attains anal velocity# v in time# t has an acceleration of SP 0'

67 8quation (1)

d.

8+ample1-

,ime ta*en for an object to fall from a height from the moon ssurface is longer than the earth s surface. &ecause g moon 9 g earth. SP 0*

e. :or motion with constant acceleration-

67 8quation (2)

67 8quation (!)

g. Motion graphs

i. ;isplacement6time graphs


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6elati%nship et-een ass and +nertia

1. cult to start a swing that carries a person inmotion compared to a vacant swing.

o ?hen the total mass of the swing is larger# the resistanceto change its initial position is greater. 4ence# when the massincreases# the inertia increases.

2. %imilarly# it is more di>cult to stop a moving swing that carriesa person compared to a vacant swing because -hen the t%talmass is larger, the resistance t% change its initial m% ementis greater . SP 0! P

8a&s t% reduce the negati e "9ect %3 +nertia2. Sa3et& easures in $ehicle t% 6educe egati e "9ect %3+nertia

i5 Seat elts @ to prevent the drivers passengers 3r%m theeing thr%-n 3%r-ard .

o increases sl%ping time

o reduce impulsi e 3%rce

o st%p the m%ti%n %3 dri er

ii. (ir ags @ prevent the driver passenger from being injured ofhitting the dashboard.

!. Ather %afety Measure


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i. Steering c%lumn @ 8asily collapsed during accident to preventit from injuring the driver.

ii. Head rests @ 'revent the head of the passengers from beingthrown bac*wards.

iii. :entre %3 #ra it& is lowered to increase the stability.

iv. Screens @ Anly crac* into small pieces and not sharp

v. "ngine @ Bollapse downward during collision.

vi. 6ein3%rced %d& structure @ to protect the passengers driver.

vii. Speed and passengers limits @ to reduce the momentum

viii. ;he 3r%nt < rear secti%ns %3 a car designed t% crumpleeasil& SP 07 @ ,o increase impact time

i+. :rumple =%ne SP 10 @ is crushed C compressed when anobstacle to lengthen collision time

+. )umper lled -ith sh%c> a s%r ers @ to minimises theimpulsive force during an incident .

!. Lorries or truc*s that carry heavy loads utilise the followingfeatures to reduce the negative eDects of inertia-


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2. ,he resistance %3 an % ect t% a change in its state %3m%ti%n is *nown as m%mentum5

!. ,he total momentum before and after the collision is the same.P10! P2S12

". ,he linear m%mentum # p of an object of mass# m# which ismoving with a velocity# v# is de ned as the pr%duct %3 mass and

el%cit& . SP P2"07 p E m + v

$. ,he unit of momentum is >g ms ?1 .

. Momentum is a ect%r @uantit& and acts in the samedirection as the velocity. ?hen the positive sign is used to representthe right direction# then the left direction is represented by thenegative sign and vice versa.

0. ?hen the velocity increase# momentum increases. SPP2"07

:%nser ati%n %3 %mentum

1. ,he principle %3 c%nser ati%n %3 m%mentum states that-that- P2S12

,he t%tal m%mentum of a system is constant#if n% e ternal 3%rce acts on the system.

2. 8+amples of e+ternal force are friction# air resistance# etc.

!. / balloon is tied to arod when the air is released# a bac*wardmomentum is produced.

". ,he principle of conservation of momentum is applied in twosituations-

a. Bollision (elastic and inelastic)

b. 8+plosion

:%llisi%ns


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!. ,he total momentum after the e+plosion is still 5ero as theupward momentum is equal to the downward momentum.

". ,herefore# the principle of conservation of momentum isobeyed.

Example 2

1. &efore e+plosion# both the bullet and the riFe are at rest. ,hetotal momentum is 5ero.

2. ?hen the riFe is red# the bullet which has mass and moveswith a velocity# produces a forward momentum. ,his causes the riFeto recoil bac*wards with a bac*ward momentum which has the

same momentum as the bullet.

,herefore# the total momentum after the e+plosion is still 5ero and it can bewritten as- m 1 v 1 G m 2 v 2 E 3 Hearranging the formula gives-


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m 1 v 1 E @ m 2 v 2 where the negative sign indicates the opposite direction. %ince themagnitudes are equal# the equation can be written as-

m 1 v 1 E @ m 2 v 2

Ather applications of e+plosions are r%c>et pr%pulsi%n and etpr%pulsi%n 3%r airplanes .Example 3

1. / running athlete

2. Momentum of the hand moving bac*wards E momentum of

the body moving forward SP 10:orce

1. / 3%rce (vector quantity) is a push or a pull on an object# unitnewton (I).

2. 8Dect of a force-

a. Moves a stationary object

b. Bhanges the velocity of a moving object in magnitude orin direction or both

c. Ban decelerate or stop a moving object

d. Bhanges the si5e of shape of an object.

!. Iewton second law of motion states that the rate of change of momentum is directl& pr%p%rti%nal to the resultant force and in

the same direction as the force.". ,o produce motion# the forward force 7 bac*ward force G

friction SP 0*

$. Mass does not eDect the force that applied that applied.


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1. ,he impulse (vector quantity) of a constant force : is de ned as the

product of the force and the time t for it acts.

2. ( g%l3er c%ntinue his s-ing a3ter hitting the allA P2"12

o

to

increase impulse on the ball

o the time of contact increase

o change of momentum increases

o the speed increases

!. +mpulse 3%rce is de ned as the rate of change of momentum.SP 07 P2 "12 '' 1" PP14

". :ront and rear sections of car designed to crumple easily# toincrease impact time. /s time of impact increases# a smallerimpulsive force results. SP 07

$. ?ays to reduce impulse force=

o ;hic> mattress will lengthen the time impact on landing#thus reducing the resultant impulsive force. SP 0*

o &as*et ball player moves his hand bac*wards whencatching the ball. ,hus# prolong the time of impact and reduce theimpulsive force acting on his palm. SP 0B

o ,he parachutist bends his *egs to lengthen the time ofimpact collision. ,his reduces the impulsive force acting on his legs.

SP 0!//11

2. ,he earth is surrounded by a gravitational eld which e+erts a forceon any body in the eld is called the force of gravity# unit I*g 61.

!. ;he 3%rce %3 gra it& acting %n an % ect is called weight (vectorquantity)# unit newton (I). SP P2S0*


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67 g E acceleration due to gravity

". Design a helmetA o Ci re glass shell

also crush on impact thus absorbing impulsive force

give better protection

o P%l&srt&rene as inside

good absorber shoc*

give protection for head

provide comfort

o Cull?3ace helmet

provide a large area of protection of head

o n%t t%% hea &

b. Bharacteristics of the rope to ma*e the parachute- PH#14


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J :orces that act on the parachute during decending- Lifting force# gravity#thrust force# dragging force

:orces in 8quilibrium 8K/M ,


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1. ?hen two forces are parallel to each other# the addition can bedone by simple arithmetic.7

a. :orces acting in the same direction

b. :orces acting in opposite directions SP 07/0'

2. Cricti%nal C%rceis force which opposes movement.

!. ?hen two forces are neither parallel nor perpendicular to ea

other# there are two methods to calculate the resultant force.

a. ;riangle meth%d P107/12?hen the forces do not start from the same point# a force diagramcan be drawn to obtain the resultant force# :H. / force diagram is arepresentation of forces with their respective magnitudes anddirections.

i. ,he diagram is drawn to a suitable scale.

ii. : 1 is drawn rst# followed by : 2 .


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iii. ,he resultant force is then drawn from the beginningof : 1 to the end of : 2

iv. ,he value of the resultant force is measured fromthe length of /B and the direction of the resultant force is 9 B/&.

b. Parallel%gram meth%d?hen the forces start from the same point# a vector diagram isdrawn to obtain the resultant force# : H.

i. / suitable scale is used in this drawing and both :1and :2 are drawn from the same point.

ii. Bomplete the drawing using a pair of compassesand then draw the diagonal of the parallelogram.

iii. ,he diagonal represents the magnitude anddirection of the resultant force# : H.

". ?hen two forces are perpendicular to each other# 'ythagorasNtheorem and the parallelogram method can be applied to obtain theresultant force.

6es%luti%n %3 C%rces

1. ,he resultant force is found by combining the forces. ,hereverse process where a single force is split into two components is*nown as the resolution of forces.


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2. ,he two components of force are the vertical force# :y and thehori5ontal force# :+. ,hey are perpendicular to each other in aparallelogram. PH#14

!. %imple trigonometry is applied to obtain the values of :+ and:y . PH#14, K14

+nclined Plane K14


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/ boy in a lift SP P2S0* '' 1"

1. ?hen the lift moves up with acceleration# the normal reactionis greater than his weight. H 7 ?# ? E mg# H @ ? E ma SP 0!

2. ,here is a resultant force acting upwards# fEma SP 07/10 en K14

a. ,ype of material of spring- Iylon (reason- strong material)

b. /ngle of pulling force# : from vertical line# O-Pse smaller angle(reason- reduce magnitude of tension of the spring)

?or* done# 8nergy# 'ower and 8>ciency 8K/M ,


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2. 8eight is gra itati%nal 3%rce (the pull of gravity) PH#14

!. ,he acceleration of all failing objects is inFuenced by the earthgra itati%nal 3%rce . SP 0B

". 8hen -eight is released, energ& changeA SP 10

,he potential energy of the weight 67 *inetic energy of the woodenbloc* C weight

$. #ra itati%nal p%tential energ& of an object is the energypossessed by the object due to its higher position in thegravitational eld.

8lasticity

1. / property of matter that enables an object to return to itsoriginal shape and si5e after the force acting on it is removed.KDH14, PH#14,

2. 4oo*eNs law states that-

,he change in length of a spring is directly proportional to the forceapplied to the spring without e+ceeding the elastic limit of the

spring. SP 0! graph Cact%rs that (9ecting the "lasticit& / Sti9ness %3 aSpring [H%%>es a-]


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linear motion.docx

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