- #1

Krushnaraj Pandya

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## Homework Statement

two discs of radii r and 2r are pressed against each other. Initially disc with radius r is rotating with angular velocity w and other disc was stationary. Both discs are hinged at their respective centers and free to rotate about them Moment of inertia of 1st disc is I and bigger disc is 2I about their respective axis of rotation, find w of bigger disc after long time. Note*-I only have a problem with one step of the solution

## Homework Equations

1) r1w1=r2w2 when slipping ceases

2) ∫(torque)dt=dL

## The Attempt at a Solution

only force producing torque about center is friction. acting upwards on the smaller disc, from equation 1 w2=w1/2 where w1 and w2 are final angular velocities of disc 1 and 2. now total angular impulse on second disk is ∫f2Rdt=dL=2Iw2....(i)

**impulse on first however is written as ∫fRdt=dL=I(w-w1)...(ii) which is initial angular momentum**round as final-initial. (i) and (ii) are later used to solve for w2 which comes out to be w/3, please explain why it is written this way and how it is correct

__minus__final angular momentum, shouldn't it be written the other way
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