Physics IX 2018 Khyber pukhtunkhwa pakistan

1. PHYSICS IX Unit 04 Ex: Conceptual Questions Writtenby
Hamid ullah( M.Sc Phy )
Q1. Can the rectangularcomponent of the vectorbe greaterthanthe vector itself?Explain.
Ans:No,the rectangularcomponentof avector can’tbe greaterthanthe vectoritself.
Because,The rectangularcomponentsof avectorare givenbythe equation
F = √ 𝑭 𝒙
𝟐 + 𝑭 𝒚
𝟐
( Where Fx and Fy are rectangularcomponentsof vector F )
Therefore, The rectangularcomponentof a vectorcan be lessthan or equal butcan’t be greater
than the Vectoritself.
Q2. Explainwhydoorhandlesare notputnear hinges?
Ans:Door handlesare notput near hinges.Because,bydefinitionof torque
Torque = Force × Perpendiculardistance fromaxisof rotation=F × d.
Fromthis relationitisclearthat torque depends onbothforce anddistance.
Therefore if we puthandlesnearhingesthenthe distance willbe zeroandhence notorque will be
Produced.
Q3. Can a small force everexertagreatertorque thana larger force?Explain.
Ans: Yesit ispossible.Because, torque isthe productof force andmomentarm.
I.e. Torque = Force × Momentarm
Fromthe above relationitisclearthat we can exertgreatertorque even byasmall force by taken
large momentarm.
Q4. Why it isbetterto use a longspannerratherthan a short one to loosenarusty nut?
Ans: Itis bettertouse a long spannertoloosena rustynut,rather than a short spanner.
Because,inthiscase the lengthof spannerisacts as momentarm, and we know that
Ƭ=F × d (where disthe momentarm)
From the above resultitisclearthat, torque increasesif momentarmincreasesandvice versa.
Q5. The gravitational force actingona satellite isalwaysdirectedtowardsthe Centreof the earth.
Doesthisforce exerttorque onsatellite?
Ans:The gravitational force actingona satellitedoesnotexertanytorque.

2. PHYSICS IX Unit 04 Ex: Conceptual Questions Writtenby
Hamid ullah( M.Sc Phy )
Because, inthiscase the gravitational force andradiusof satellite are anti paralleltoeachother.
And bydefinitionof torque Ƭ=FdsinƟ (where dis the momentarm = radiusof satellite)
Put Ɵ = 1800
. thenabove equationbecomes Ƭ =Fdsin1800
=Fd(0) =0 ( because sin1800
=0 )
Such type of force iscalledcentral force.
Q6. Can we have a situationsinwhich anobjectisnotequilibrium, eventhoughthe netforce onitis
zero? Give two examples.
Ans:For a body to be incomplete equilibriumonlyif it satisfiedthe followingtwoconditions.
1st
condition Ʃ 𝑭 = 𝟎 and 2nd
condition Ʃ Ƭ =0
Therefore,if abody satisfiedthe 1st
conditionbutdoesnotsatisfiedthe 2nd
conditionthenitwill be not
inequilibrium.
Example i) Whenthe pedalsof bicycle are rotated,inthiscase Ʃ 𝑭 = 𝟎 and ƩƬ ≠ 0. That’swhyit is
not inequilibrium.
ii) Whenthe steeringwheelof acar isrotated,in thiscase Ʃ 𝑭 = 𝟎 and ƩƬ ≠ 0. That’swhyit isnot in
equilibrium.
Q7. Why do tightrope walkercarrya long,narrow rod?
Ans:A tightrope walkeruse longnarrowrodforgettingbalancedcondition andpreventhimself from
fallingthe rope.
Because,if the tightrope walkerleanstowardsrightandproduce clockwise torque thenhe wantsto
maintain its state of equilibrium and produces anticlockwise torque with the help of narrow rod.
Q8. Why does wearing high heeled shoes sometimes cause lower back pain?
Ans:Because,withhighheeledshoessomeonepushthe bodyinthe forwarddirectiondue towhichthe
Centre of gravityof the body disturbed.Tomaintainbalancedconditionthe bodytrytooppose the
forwardpushof the highheeledshoes.Insuchefforthismusclesbecomestense andhe feelsbackpain.
Q9. Why it ismore difficulttoleanbackwards.Explain?
Ans:Because,toleanbackwardthe Centre of gravityof a body is disturbed,due towhichthe unstability
increases anditbecomesdifficultforabodyto maintainitsstate of equilibrium.
Q10. Can a single force appliedtoa bodychange bothits translational androtational motion?Explain.
Ans:Yes a single force canchange both translational motionandrotational of abody if itis appliedat
any otherpointnotcentre of mass.

3. PHYSICS IX Unit 04 Ex: Conceptual Questions Writtenby
Hamid ullah( M.Sc Phy )
Explanation: Because,we knowthat force can change onlytranslational motionif itisappliedatthe
Centre of mass of a body,and force can change both translational androtational motionof abodyif it
isappliedatany otherpointnotcentre of mass.
Q11. Two forcesproduce the same torque.Doesitfollow thattheyhave the same magnitude?Explain.
Describe the pathof the brickafteryou suddenlylet goof the rope.
Ans:It may or may notbe same.Because, Ƭ =FdsinƟ ( A )
From equation(A) itisclearthat,torque notonlydependonforce but alsodependsonmomentarm
and angle betweenthem.Formore convenience putƟ= 900
, thenequation(A) becomes Ƭ=Fd. So
torque isthe product of force andMoment arm. Therefore we canproduce same torque by putting
differentvaluesof Fandd.
Example: a) Ƭ=Fd, putF=12N and d=2m, then Ƭ= 12×2=24Nm
b) PutF=8N andd=3m, thenƬ =8×3=24Nm
if the rope issuddenlyletgooff,thenthe brick movesawayalongtangenttothe circular path.
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4. PHYSICS IX Unit 04 Ex: Conceptual Questions Writtenby
Hamid ullah( M.Sc Phy )