1 Rotational Motion
A ring of mass M and radius R is rotating with angular speed ω about a fixed vertical axis passing through its centre O with two point masses each of mass M / 8 at rest at O. These masses can move radially outwards along two massless rods fixed on the ring as shown in the figure. At some instant the angular speed of the system is 8ω/9 and one of the masses is at a distance of 3R/5 from O. At this instant the distance of the other mass from O is
1) 2R/3 2) R/3 3) 3R/5 4) 4R/5
SOLUTION : Let the other mass be at a distance x from the centre. Conserving angular momentum about the axis :
on solving x =4R/5
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