physics chemistry maths science forums
become expert I help I sign up I login
refer a friend - earn nickels!!   
 advanced
 
Home
Ask & Discuss Questions
Study Material
Experts Zone
Hang Out!

Ask & Discuss Questions with Community & Experts

 Moderation Team
 90 chars left    advanced
Ask iit jee aieee pet cbse icse state board community Community Discussion Question: Challenge - rotational mechanics
Forum Index -> Mechanics like the article? email it to a friend.  
Author Message
[Post New]3 Jan 2008 20:58:23 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)

Blazing goIITian

Olaaa!! Perrrfect answer. 591  [788 rates]
karthik2007's Avatar
total posts: 2585    
offline Offline
A solid sphere of mass M and radius R initially rotating with angular velocity o in anti clockwise direction is gently placed between smooth inclined plane having angle @ and ground as shown in figure. If coefficient of friction between the sphere and the ground is k, then find the time t after which rotation of the sphere ceases.

Will nip in at times to solve problems :)
    
[Post New]3 Jan 2008 21:01:26 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)

Blazing goIITian

Olaaa!! Perrrfect answer. 591  [788 rates]
karthik2007's Avatar
total posts: 2585    
offline Offline
answer will be posted tomorrow if no one is able to solve this
Will nip in at times to solve problems :)
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 21:27:24 IST
    Subject: Re:Challenge - rotational mechanics
[Up] View Post
srk (10)

New kid on the Block

Olaaa!! Perrrfect answer. 2  [2 rates]
srk's Avatar
total posts: 13    
offline Offline
is the answer t=wI(sec-cosec)/kmgsecr
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 21:30:45 IST
    Subject: Re:Challenge - rotational mechanics
[Up] View Post
Raghudevan (135)

Blazing goIITian

Olaaa!! Perrrfect answer. 19  [39 rates]
Raghudevan's Avatar
total posts: 325    
offline Offline
sphere is already rotaing with some  so the sphere will have a tendency to move in the rightward direcrtion so friction will act leftwards.
 
f = k(mg)
 
a torque is produced by friction, it causes an angular retadation   
 
 = /I
   
   = 5kg/2R
 
so,
 
0 =  - (5kg/2R)t
 
so,
 
t = (2R)/5Kg     
 
the other smooth surface that the sphere is in contact with will only disable the sphere from moving leftwards.
 
i dont know if this is correct., waiting for conformation from Karthik2007:)
S.Raghudevan

Everything that's happening as it should be happening, because of the simple fact that it's supposed to be happening just as it is happening.
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 21:56:03 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)

Blazing goIITian

Olaaa!! Perrrfect answer. 591  [788 rates]
karthik2007's Avatar
total posts: 2585    
offline Offline
sorry... none are correct
Will nip in at times to solve problems :)
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 22:10:27 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)

Blazing goIITian

Olaaa!! Perrrfect answer. 591  [788 rates]
karthik2007's Avatar
total posts: 2585    
offline Offline
3 salutes for the correct answer
Will nip in at times to solve problems :)
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 22:11:58 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
Raghudevan (135)

Blazing goIITian

Olaaa!! Perrrfect answer. 19  [39 rates]
Raghudevan's Avatar
total posts: 325    
offline Offline
can i know where i have gone wrong
S.Raghudevan

Everything that's happening as it should be happening, because of the simple fact that it's supposed to be happening just as it is happening.
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 22:27:16 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)

Blazing goIITian

Olaaa!! Perrrfect answer. 591  [788 rates]
karthik2007's Avatar
total posts: 2585    
offline Offline
You are wrong in the statement where you've found the force of friction... you have got the Normal reactions wrong
Will nip in at times to solve problems :)
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 23:40:20 IST
    Subject: Re:Challenge - rotational mechanics
[Up] View Post
rohith291991 (511)

Blazing goIITian

Olaaa!! Perrrfect answer. 91  [119 rates]
rohith291991's Avatar
total posts: 427    
offline Offline
t=2oR((1+k2)sinA)/5kg(k(1+cosA)+sinA) if both surfaces have fricton otherwise...
t=2oR(1-kcotA)/5kg
Be Strong Be Different. Just Be


 this reply: 2 points  (with 0 Olaaa!! Perrrfect answer.   in 1 votes )   [?]
 
You have to be logged on to rate
  
[Post New]3 Jan 2008 23:43:45 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)

Blazing goIITian

Olaaa!! Perrrfect answer. 591  [788 rates]
karthik2007's Avatar
total posts: 2585    
offline Offline
Nopes :(
Will nip in at times to solve problems :)
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]4 Jan 2008 00:06:22 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
madman (239)

Blazing goIITian

Olaaa!! Perrrfect answer. 33  [70 rates]
madman's Avatar
total posts: 486    
offline Offline
I got R(2/5-cos@sin@)w/gk
science-
the most fundamental
the most eternal
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]4 Jan 2008 00:08:11 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
madman (239)

Blazing goIITian

Olaaa!! Perrrfect answer. 33  [70 rates]
madman's Avatar
total posts: 486    
offline Offline
is it correct
science-
the most fundamental
the most eternal
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]4 Jan 2008 00:31:14 IST
    Subject: Re:Challenge - rotational mechanics
[Up] View Post
rohith291991 (511)

Blazing goIITian

Olaaa!! Perrrfect answer. 91  [119 rates]
rohith291991's Avatar
total posts: 427    
offline Offline
hey karthik2007 reply man am i correct??
Be Strong Be Different. Just Be


 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]4 Jan 2008 00:49:20 IST
    Subject: Re:Challenge - rotational mechanics
[Up] View Post
rooney (889)

Blazing goIITian

Olaaa!! Perrrfect answer. 151  bad job dude!! I dont approve of this answer! 1  [220 rates]
rooney's Avatar
total posts: 577    
offline Offline
Let N be the normal force of upper surface with sphere and R be that of lower surface. So, kR is frictional force on the sphere by the ground towards the left.

Balance forces on both axis,
kR=Nsin
NCos + Mg=R

Replacing N from 1 eq to the other, we get R =Mg/(1-kCot)
So, friction = kR
Torque = Ia = kRr
2Mr2a/5 = kMg/(1-kCot)
a=5kg/2r(1-kCot) = angular deceleration
 =>0 =   0 - at
t = 20r(1-kCot)/5kg

So, rohith291991's answer is right.
http://14-69-8.blogspot.com
My blog
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]4 Jan 2008 02:32:16 IST
    Subject: Challenge - rotational mechanics
[Up] View Post
karthik2007 (3349)