Moderate -->Circular Motion

An circular Iron rod of radius r is put into an inverted cone which rotates with an angular velocity 'w'. If the mass of the ring me M find the tension in the the Iron rod if it rotates with the the cone without sliding. Neglect any friction.
Given Semi angle =( theta )

6 Answers

62
Lokesh Verma ·

draw the fbd of a small element which subtends and angle dα at the center...

The length of the element will be r.dα

Now the acceleration of the rod is w2r towards the center..

balance the forces to get mg=Nsinθ

N cos θ + 2Tsin(dα/2) = m w2r

From the above two equations...

mg cotθ +2T dα = m w2r

Also, 4r dα λ = m (where λ is the mass per unit length)

So, 4r dα λ g cotθ +2T dα = 4r dα λ w2r

T = 2r λ w2r - 2rλ g cotθ
Where λ*2πr = M

So T= (w2r - g cotθ)/π

71
Vivek @ Born this Way ·

So the tension is the same as the force on any arbitrarily small part of the chain (Of course due to Cone). That's the idea I got it.

1
abhishek arora ·

i think you made some mistakes above
1) m= r dα λ and not m= 4 r dα λ

2) N cosθ +2T dα/2 = mw2r when you make assumption and not
N cosθ +2T dα = mw2r

please correct me if i am wrong.......................

1
varun.tinkle ·

for the concept just remem. how we derived speed of a trnasverse wave the same concept is applied here...

71
Vivek @ Born this Way ·

derived speed of a trnasverse wave the same concept is applied here!

Haven't read that yet!

71
Vivek @ Born this Way ·

@ abhishek. I don't know the answer. Basically I just ask for questions and the answers to anyone. So i can't explain whether it is matching or not.

But I think you're correct since why should be put 4 there.?

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