Posted by **Patricia** on Thursday, November 7, 2013 at 6:40pm.

A student on a piano stool rotates freely with an angular speed of 2.85rev/s . The student holds a 1.10kg mass in each outstretched arm, 0.789m from the axis of rotation. The combined moment of inertia of the student and the stool, ignoring the two masses, is 5.23kg⋅m2 , a value that remains constant.

--> As the student pulls his arms inward, his angular speed increases to 3.45rev/s . How far are the masses from the axis of rotation at this time, considering the masses to be points?

-->Calculate the initial kinetic energy of the system.

-->Calculate the final kinetic energy of the system.

- Physics -
**bobpursley**, Thursday, November 7, 2013 at 6:59pm
Calculate the moment of inertia for the masses (2*mr^2)

now the student I and the mass I add to give Itotal, both in the initial Itotali, and the final Itotalf where one of them has a different radius0

conservation of momentum applies

Intial momentum=final momentum

(Itotali*2PI*2.85)=Itotalf*2PI*(3.45)

notice the 2PI divide out, so now solve for rfinal in the Itotalf.

iniial KE=1/2 Itotali*(2PI*2.85)^2 and similar for final KE

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