# Physics

posted by .

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 -

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

## Similar Questions

1. ### physic

A student on a piano stool rotates freely with an angular speed of 3.07 rev/s. The student holds a 1.38 kg mass in each outstretched arm, 0.759 m from the axis of rotation. The combined moment of inertia of the student and the stool, …
2. ### physics

A student sits at rest on a piano stool that can rotate without friction. The moment of inertia of the student-stool system is 4.6 kg m^2. A second student tosses a 1.5 kg mass with a speed of 2.9 m/s to the student on the stool, who …
3. ### physics

A student sits at rest on a piano stool that can rotate without friction. The moment of inertia of the student-stool system is 4.2 . A second student tosses a 1.1 mass with a speed of 3.0 to the student on the stool, who catches it …
4. ### physics

A student sits at rest on a piano stool that can rotate without friction. The moment of inertia of the student-stool system is 4.6 kg m^2. A second student tosses a 1.5 kg mass with a speed of 2.9 m/s to the student on the stool, who …
5. ### Physics

A student on a piano stool rotates freely with an angular speed of 2.95 rad/s . The student holds a 1.35 kg mass in each outstretched arm, 0.739 m from the axis of rotation. The combined moment of inertia of the student and the stool, …
6. ### Physics

A student sits on a rotating stool holding two 3.4-kg objects. When his arms are extended horizontally, the objects are 1.0 m from the axis of rotation and he rotates with an angular speed of 0.75 rad/s. The moment of inertia of the …
7. ### physics !!

A student on a stool rotates freely at 180 rounds per minute. The student holds a 1.00 kg mass in each outstretched arm, 0.8 m from the axis of rotation. The combined moment of inertia of the student and the stool is 6.00 kgm2 which …
8. ### physics

A student holds two lead weights, each of mass 12 kg. When the studentsâ€™ arms are extended horizontally, the lead weights are 0.82 m from the axis of rotation and the student rotates with an angular speed of 1.5 rad/sec. The moment …
9. ### ap physics

A student sits on a rotating stool holding two 3.8-kg objects. When his arms are extended horizontally, the objects are 1.0 m from the axis of rotation and he rotates with an angular speed of 0.75 rad/s. The moment of inertia of the …
10. ### Physics

A student on a piano stool rotates freely with an angular speed of 3.07 rev/s. The student holds a 1.38 kg mass in each outstretched arm, 0.759 m from the axis of rotation. The combined moment of inertia of the student and the stool, …

More Similar Questions