A child is standing with hands straight down at thecentre of a platform rotating about its central axis The kinetic - Physics - System of particles and rotational motion

Question

A child is standing with hands straight down at thecentre of a
platform rotating about its central axis The kinetic energy of the
system is K The child nowstretches his arms so that the moment of
inertia ofthe system doubles The kinetic energy of thesystem now is

4k
k/4
k/2
2k

Ved Prakash Lakhera · Accepted Answer

Let the M  I
 and angular speed of the system be I and ω respectively
The kinetic energy of the system given   K=12Iω2
When the system is rotating then             Iω=2I×ω0or          ω0=ω2So new kinetic energy of the system is  K
 E
 = 12×2I×ω22or              K
 E
 = 12×2I×ω24=12×12Iω2=K2Therefore the correct answer is option 3 K2

A child is standing with hands straight down at thecentre of a platform rotating about its central axis.The kinetic energy of the system is K. The child nowstretches his arms so that the moment of inertia ofthe system doubles. The kinetic energy of thesystem now is 4k k/4 k/2 2k

A child is standing with hands straight down at thecentre of a platform rotating about its central axis.The kinetic energy of the system is K. The child nowstretches his arms so that the moment of inertia ofthe system doubles. The kinetic energy of thesystem now is

4k

k/4

k/2

2k