A boy is seated in a revolving chair revolving at an angular speed of 120 revolutions per minute. Two heavy balls form part of the revolving system and the boy can pull the balls closer to himself or may push them apart. If by pulling the balls closer, the boy decreases the moment of inertia of the system from `6 kg-m^2 to 2 kg-m^2` what will 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