A student sits on a rotating stool holding two 5 kg objects. When his arms are extended horizontally, the objects are 0.9 m from the axis of rotation, and he rotates with angular speed of 0.66 rad/sec. The moment of inertia of the student plus the stool is 8 kg m2 and is assumed to be constant. The student then pulls the objects horizontally to a radius 0.31 m from the rotation axis. Calculate the final angular speed of the student.

Respuesta :

Answer:[tex]\omega _f=1.185\ rad/s[/tex]

Explanation:

Given

mass of objects [tex]m=5\ kg[/tex]

Initially mass is at [tex]r=0.9\ m[/tex]

Initial angular speed [tex]\omega_i=0.66\ rad/s[/tex]

Moment of inertia of student and  stool is [tex]I_s=8\ kg-m^2[/tex]

Finally masses are at a distance of [tex]r_f=0.31\ m[/tex] from axis

[tex]I_i=I_p+I_m[/tex]

[tex]I_i=8+2\times 5\times (0.9)^2[/tex]

[tex]I_i=16.1\ kg-m^2[/tex]

Final moment of inertia of the system

[tex]I_f=I_s+I_m[/tex]

[tex]I_f=8+2\times 5\times (0.31)^2[/tex]

[tex]I_f=8+0.961=8.961\ kg-m^2[/tex]

As there is no external torque therefore moment of inertia is conserved

[tex]I_i\omega _i=I_f\omega _f[/tex]

[tex]\omega _f=\frac{16.1}{8.96}\times 0.66[/tex]

[tex]\omega _f=1.796\times 0.66[/tex]

[tex]\omega _f=1.185\ rad/s[/tex]

Q&A Education