IIT JEE , AIEEE Forum - Physics , Mechanics

zeeshanp

i am realy confused regardin question 4 and 5.................
i though avg velocity=displacement /t2-t1...........dats da definition given in da hcverma..........
but in question number 4 avg vel =v1+v2/2
and in question 5 .....2/v=1/v1 + 1/v2........
how did they get all they answers...........pls explain!!

sandeepramesh

If there is constant accelaration, then the avg velocity over time can be obtained as (v1+v2)/2 where v1 and v2 are the initial n final velocities :)

zeeshanp

the man is travelling wid uniform velocity.............so der is no question of accelelretion!!!!!

destinationIIT09

4)

total time taken be t

displacement in first time =v1t/2

displacement in second equal time=v2t/2

average velocity =total dispacement /total time

=(v1t/2+v2t/2) / t

=(v1+v2)/2

Sushmi

Check what is given in the question :

"A person travelling on a straight line moves with uniform vel v1 for sometime and uniform velocity v2 for next equal time "

So v . t = v1 . t/2 + v2 . t/2

hence v =(v1 + v2)/2

Then its given that "v1 for dist x and uniform velocity v2 for dist x"

So you have to equate time

So 2x/ v = x/v1 + x/v2

So 2/v = 1/v1 + 1/v2

destinationIIT09

5)

total displacement=2x

total time taken =x/v1 + x/v2

average velocity,v= 2x/(x/v1+ x/v2)

2/v = 1/v1 + 1/v2

zeeshanp

@ destinationIIT09
in da question 4 its mentioned da inderval is same so how did u take da displacement to be da same,,,,,,,,??
da displacement is da same in da next question.............

destinationIIT09

i never took displacement as the same

jus took the total time interval as t

then first time interval becomes t/2 and so is second

I AM A NEWCOMER

SO PLZZZ DO RATE IF FOUND USEFUL

Sushmi

You have to equate the total displ dear......

let time for which it moves in vel v1 = t

time for which it moves in vel for next half wid vel v2= t

so total time = 2t

hence equate displ

v . 2t = v1 . t + v2 . t

so v = (v1 + v2)/2

sandeepramesh

sorry, i didnt see the question from HCV at all :) Anyways as someone said, if its travelling with unif vel, then its clearly v1+v2/2 as its for equal times :)

destinationIIT09

@ZEESHAMP

THIS MIGHT CLEAR UR CONCEPTS ABT AVERAGE VELOCITY BETTER

-if y (maybe velocity,maybe acceleration) is a function of itme

y= f(t)

and we want 2 find average value of y between a time interval t1 and t2

<y> t1 to t2 = integral of f(t) dt within the limits t1 and t2 /( t2- t1)

----here v is a linear function of time

hence average velocity =[ u{initial} + v{final} ] /2

HOPE ITS USEFUL

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