NEET Physics Mathematical Tools Questions Solved


Two discs of radii R and 2R are pressed against each other. Initially disc with radius R is rotating with angular velocity ω and other disc was stationary. Both disc are hinged at their respective centres and free to rotate about them.Moment of inertia of smaller is I and bigger disc is 2I about their respective axis of rotation. Find the angular velocity of the bigger disc after long time. 

   [This question is only for Dropper and XII batch]

 

                     

1. ω

2. ω/2

3. ω/3

4. 2ω3

Concept Videos :-

#16 | Calculus: Differential Equation
#19 | Numericals

Concept Questions :-

The only force which is producing any torque about the centre of first disk is friction. Let the disc rotates with angular velocity  as shown.

                                

Now, ω1R = ω2×2R as the point in contact should have same velocity after stops.ω2=ω12Now, total angular impulse provide by the friction is equal to change in angular momentum of the discfRdt= I(ω-ω1)         and           f2Rdt= 2Iω2           2I(ω-ω1) = 2Iω2         ω1+ω2=ω             2ω2+ω2=ω            ω2=ω3

Difficulty Level:

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