Two Sided Pulley!

There is a light, inelastic thread is stretched round one half of the circumference of a fixed cylinder as shown above.

As a result of friction, the thread does not slip on the cylinder when the magnitudes of the forces acting on the ends satisfy the inequality 1 2 F A F B 2 F A \frac{1}{2}F_A\le F_B\le 2F_A

Determine the coefficient of friction μ \mu between the thread and the cylinder.


The answer is 0.2206356.

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1 solution

Now, F A = F 0 , F B = F ( π ) = F 0 e μ π \displaystyle F_A = F_0,~F_B = F(\pi) = F_0e^{\mu\pi}

If 1 2 F A F B , then, μ 0 [ Not possible ] \text{If } \dfrac{1}{2}F_A \le F_B, \text{ then, } \mu\le 0~~[\text{Not possible}]

Else F b 2 F A μ 1 π ln 2 \text{Else } F_b \le 2F_A\Rightarrow \mu \le \dfrac{1}{\pi}\ln 2

We need maximum μ \mu because friction always balances d F \mathrm{d}F

μ = 1 π ln 2 \Large \therefore \boxed{\mu = \dfrac{1}{\pi}\ln 2}

CreDit : 200 Puzzling Physics Problems

It is also called Euler's relation.

P.S:- I did an experimental verification of this at OCSC.

Rajdeep Dhingra - 5 years ago

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Did you plot something like a e^x graph?

Swapnil Das - 3 years, 5 months ago

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Yeah, first we collected data then we did graph plotting to verify the relation.

Rajdeep Dhingra - 3 years, 4 months ago

Your problems are really challenging and nice. Are these original?

Jayakumar Krishnan - 5 years, 8 months ago

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No. They are not original man. I heard from some one that these are from FIITJEE book.

Surya Prakash - 5 years, 8 months ago

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Nope these aren't from FIITJEE books... Don't just assume like this...

Kishore S. Shenoy - 5 years, 8 months ago

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@Kishore S. Shenoy Okay man. No offense. Only defence :P

Surya Prakash - 5 years, 8 months ago

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@Surya Prakash Hehe. No problem!

Kishore S. Shenoy - 5 years, 8 months ago

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@Kishore S. Shenoy Hey. I have a doubt. Are the problems from FIITJEE book very nice , i mean like are they awesome?

Surya Prakash - 5 years, 8 months ago

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@Surya Prakash Two or three in a chapter textbook.

Kishore S. Shenoy - 5 years, 8 months ago

I get good questions from different sources and post it so that it can help others too... ¨ \ddot\smile

Kishore S. Shenoy - 5 years, 8 months ago

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It would be nice if you could credit the source too. You seem to have an incredible knowledge in mechanics.

Jayakumar Krishnan - 5 years, 8 months ago

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@Jayakumar Krishnan Me? Don't think so! What we know is just a drop!

Kishore S. Shenoy - 5 years, 8 months ago

@Jayakumar Krishnan Done! Thank you!

Kishore S. Shenoy - 5 years, 8 months ago

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