A boy is seated in as revolving chair revolving at an angulr speed of 120 revolutions per minute. Two heavy balls from part of the revolving system and the boy can poull the balls closer to himself or may push them apart. If by pulling the bals closer, the boy decreases the moment of inertia fo th system from `6 kg-m^2 to kg-m^2` what wil be the new angular speed?

Answer

C

Explanation

`omega_1=120rpm=120xx((2r)/60)`
`=-4rrad/s`
`I_1=6kg-m^2,I_2=2kg-m^2`
since two balls are inside the system, total exterN/Al torque =-0`
Therefore `I_1omega_1=I_2omega_2`
`rarr 6xx4r=2omega_2`
`rarr omega_2=12r rad/s`
`=6rev/s `
`=360rev/minute