Physics IX 2018 Khyber pukhtunkhwa pakistan

1. PHYSICSIX: Unit03 Dynamics (2018) By
Ex: Conceptual Questions Hamidullah(sps)
Q2.
Ans:We can remove some waterfromourwethands byshakingthem.Itis due to inertia.
Whenwe shake our hands,the handsstart motion,while the dropsof waterare at rest and wants to
remainat rest,due to inertiathese dropsdetachedfromhands.
Q5.
Ans:Whena car stuck ina wetmud,itis difficulttocome out the car frommudbecause the force of
frictionisminimumbetweenthe tyresandthe wetmud. To increase friction,normal force onthe
car mustbe increases.That is f=µFn . That’s whythe studentssitonthe trunk of the car to increase
frictionandeasilycome outthe car from wetmud.
Q6.
Ans:walkingispossibleonlybecause of friction.AccordingNewton’s3rd
law of motion whenwe
walkwe pushesthe groundbackward,as a reactionthe groundpushesusforward.Withoutfriction
it isnot possible forustowalkon the ground, because withoutfriction we can’tpushesthe ground
hard inbackward. This isstaticfrictionwhichenable ustowalkon the ground.
Q7. The parkingbrake on a car causesthe rear wheelstolockup.
While drivingfastona road,if the parkingbrake isappliedthe rearwheels lockupwhilethe front
wheelsare inmotionand wantto maintainitsmotiondue toinertia.So the car will skid insuch
situation.
Q11.
Ans:Whenwe tie a brickto the endof rope and whirl itinhorizontal circle we provide centripetal
force to the brick whichpulledittowardthe centerof the circle.Asa reactioncentrifugal force also
exertsonour handswhichwantto move awaythe brickfromthe centerof circle.
Nowif we letgo the rope suddenly,the brickmove alongtangent tothe circle due to itstangential
velocity.
Q12
Ans:To turn a car we need more centripetal force,whichisprovidedbythe frictionalforce between
the road and the tyres.Duringturning, the speedmustbe lowerthanthe normal speed.If we
increasesthe speedfromthat limitthenthe centripetal force will notbe sufficientforsafe turnand
the car will skidaway fromthe road causesaccident.