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A highly expexted good question for JEE which is made by me with a GREAT MIND.

Find the tension in the thread at the last block placed at infinity.
Each block is of mass m and the masses of the thread and pulleys are negligible.

18 Answers

1
Banned User ·

Kaymant sir , plzzzzz check whether ans given by Arshad is right or not ????

1
$ourav @@@ -- WILL Never give ·

n by d way arshad,wat formula hav u applied.....sum of infinite g.p is =a/(1-r)
here according to u a=t and r=1/2,,,so sum is=t/{1-(1/2)}....it comes as 2t newton and not 2 newton...
............isnt it arshad???

1
Bicchuram Aveek ·

Someone pleeeeeeeeeeease describe this.

1
Bicchuram Aveek ·

Pls describe how

1
Arshad ~Died~ ·

yup i realized my mistake...
the acceleration of left side block is coming out to be g/2

1
Philip Calvert ·

Arshad u are underestimating the question to an alarming degree

also your method of summing all the tensions on one side is physically insignificant

1
Philip Calvert ·

On solving we get the acceleration of the topmost block as g/2 (actually all the blocks move with this acceleration upwards in their respective frames)

My solution is a bit tedious to write without latex,

if no one else posts the correct solution then I will do so.

1
Arshad ~Died~ ·

sir actually i missed one brackett..
what i wanted to write was that sum of an infinte gp=
t/(1-(t/2))=2

66
kaymant ·

No, arshad's answer is not correct.

@arshad, how does t/1-(t/2) becomes 2 N

66
kaymant ·

I'll add to the problem: Find the acceleration of the topmost block on the left.

(And this question is not going to come in IIT JEE)

1
Arshad ~Died~ ·

and eureka the feyman lectures one is a bit different....
here the masses are given to be equal....

1
Arshad ~Died~ ·

i think yes sir....if we consider the tension to be in newton....

24
eureka123 ·

got it..
its in feynmann lectures.. [1]

66
kaymant ·

@arshad
is ur answer dimensionally consistent?

1
Philip Calvert ·

It is actually a well known problem

24
eureka123 ·

Its an olympiad question as far as I remember [12]

1
Arshad ~Died~ ·

tension in each succesive pulley varies by a factor of t/2
so its forming an infinite gp like t,t/2,t/4........
hence the tension in the infinite pulley will be 0....
now kaymant sirs question
total tension in the right side=t/1-(t/2) =2 N
so acceleration of topmost block on the left a=(mg-2)/m

1
Banned User ·

Thanx Anant sir, for making the ques more complicated and interesting.

Why this ques is not going to come in jee? These type of questions should come in JEE

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