# A doubt

Note by A Former Brilliant Member
3 years, 7 months ago

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Sort by:

- 3 years, 3 months ago

Thanks!!!

- 3 years, 3 months ago

- 3 years, 7 months ago

- 3 years, 7 months ago

Thanks for the q.let me try.

- 3 years, 7 months ago

Has anybody solved this yet?

- 3 years, 7 months ago

Any ideas guyzzz????

- 3 years, 7 months ago

Tan(Equlibruim angle)= (ur)/(l+r) Is that right ??

- 3 years, 7 months ago

Torque applies here??

- 3 years, 6 months ago

Neat. I like this. I have to go now, but will come back and check this.

The way to approach this is to think equilibrium. If the thin rod is not moving, then it is in equilibrium. All torques (taken about any convenient point must sum to zero. And all forces must sum to zero.

Let mu the coefficient of friction be u... So imagine that u is large and the rod is horizontal. The CCW rotating axle gives the hoop a leftward pointing force. Take torques about the center of the hoop. That force is mu* m * g and it makes a torque out of the page equal to

r * u * m * g The bob makes a torque = m * g * (l+r) sine (theta) into the page and that is equal to the first torque.

So sine (theta) = r * u * m * g / ( m * g * ( l+r) ) = r * u / ( l+r)

Thus theta = arcsine ( r * u / ( l+r ) ) This is true for the hoop touching the axle at the top of the hoop.

it will touch at an angle though, and that will make the mg break into components, in the r * u * m * g part. So that is messier. I will come back to this.

- 3 years, 5 months ago

I'm facing a problem regarding which books to refer, A Das Gupta or Cengage (As subjective might make me slow and objective might not ensure conceptual clarity). Could you kindly comment?

- 3 years, 3 months ago

i actually use cengage for both physics and maths. Cengage has quite a good number of subjective questions in each chapter,so you should not worry about conceptual clarity.

- 3 years, 3 months ago

Thanks!

- 3 years, 3 months ago