This document contains conceptual questions and answers about kinematics from a Physics Class IX textbook. It discusses topics like: 1) The difference between displacement and distance, and when displacement equals distance. Displacement accounts for direction of motion while distance does not. 2) That a speedometer measures speed, not velocity, as it does not account for direction of motion. 3) How an object can be accelerating and at rest at the same time, using the example of an object thrown vertically upward reaching its peak. 4) How an object can have zero acceleration but non-zero velocity if it is moving at a constant velocity. 5) That a ball dropped from a building has an acceleration

1. PHYSICS CLASS IX ( New Course 2018 ) UNIT# 02 KINEMATICS
EX: CONCEPTUAL QUESTIONS
Written By HAMID ULLAH (M.Sc Phy)
Q1. Is it possible thatdisplacementiszerobutnotthe distance?Underwhatconditiondisplacementwill
be equal to distance.
Ans:The distance isthe lengthof total pathwithno specificdirection,while displacementisthe length
of shortestpathwithspecificdirection.Therefore if abodyismovingalonganyclosedpathand comes
back to itsstartingpoint.Thenit will coversome distance whileitsdisplacementwill be zero.
Displacementwill be equal todistance onlyif abody ismovingalonga straightand doesnotcome back
or reverse.
Q2.Doesspeedometermeasure acar’sspeedorvelocity?
Ans:Velocity meansspeedinaparticulardirection.The speedometeronlymeasure the magnitude of
velocitythatisonlymeasuredspeed.
Q3. Is it possible foran objecttobe accelerating andat rest at the same time?Explainwithexample.
Ans:By definitionof acceleration
a=Δv/Δt
If v=0 thenΔv=0 Therefore a=0
Special Case: Whena body isthrownverticallyupward,it reachto a certainheightthencome back
to the ground. At thishighestpointitsvelocityiszerobut still ithasacceleration due togravity.
Q4. Can an objecthave zeroaccelerationand non-zerovelocityatthe same time?Give example.
Ans:Accelerationisthe time rate of change of velocity.
Therefore if body ismovingwithconstantvelocitythenitsaccelerationiszero.
Mathematically a=Δv/Δt
If v=constantthenΔv=0
Therefore a=0
Q5. A personstandingonthe roof of buildingthrowsarubber ball downwithof velocityof 8ms-1
.What
Is the acceleration (magnitude anddirectionof aball?
Ans:In givenexampleif we ignoredthe airresistance,thenthe accelerationof the ball willbe constant,
such accelerationiscalledgravitationalaccelerationitsvalue is9.8ms-2
anditis alwaysdirectedtoward
the Centre of the earth.
Q6. Describe a situationinwhichthe speedof anobjectisconstantwhile the velocityis not.
Ans:If a bodyis movingalongacircular pathwithuniformspeedthenthe directionof the velocity
changescontinuously.Therefore itsspeedisconstantbutnotthe velocity.
Q7. Can an objecthave northwardvelocityandasouthwardacceleration?Explain.

2. PHYSICS CLASS IX ( New Course 2018 ) UNIT# 02 KINEMATICS
EX: CONCEPTUAL QUESTIONS
Written By HAMID ULLAH (M.Sc Phy)
Ans:Yes, if a car ismovingalonga straightpathwithcertainvelocitytowards north, if suddenlythe
driverof the car appliesthe brake itsvelocitydecreaseswithtime producesacceleration inthe opposite
directionthat’stowardsouth.
Q8. As a free fallingobjectspeedsup, whatishappeningtoitsacceleration- doesitincrease,decrease,
Or stay the same?
Ans:The motioninwhichthe air resistance isnegligibleandthe accelerationisnearlyconstant,isknown
as free fall.Thereforethe accelerationof the free fallingobjectwill remainthe same.
Q9. A ball isthrownverticallyupward withaninitial speedof 5ms-1
.Whatwill itsspeedwhenit returns
to startingpoint?
Ans:In the givenProblemif we ignore the airresistance thenthe ball will returnstoitsstartingpoint
withthe same speed.I.e.V=5ms-1
.