Two thin rods of length L are rotating with the same angular speed ω (in rad/s) about axes that pass perpendicularly through one end. Rod A is massless but has a particle of mass 0.75 kg attached to its free end. Rod B has a mass of 0.75 kg, which is distributed uniformly along its length. The length of each rod is 0.87 m, and the angular speed is 4.6 rad/s. Find the kinetic energies of rod A with its attached particle and of rod B.

Respuesta :

Answer:

a) 6.0 J

b) 2.0 J

Explanation:

The kinetic energy in this case is given by:

[tex]K=\frac{1}{2}*I*\omega^2[/tex]

where I is the moment of inertia, for both cases the moment of inertia is different.

For case A the moment of inertia of a particle is given by:

[tex]I=M*r^2[/tex]

and for B

[tex]I=\frac{1}{3}M*L^2[/tex]

Solving this:

[tex]K_a=\frac{1}{2}*(0.75kg*(0.87m)^2)*(4.6rad/s)^2\\\\K_a=6.0J\\\\K_a=\frac{1}{2}*(\frac{1}{3}*0.75kg*(0.87m)^2)*(4.6rad/s)^2\\\\K_a=2.0J[/tex]

(a) The kinetic energy of rod A is 6.0 J

(b) The kinetic energy of rod B is 2.0 J

Rotational Motion:

The kinetic energy in rotational motion is given by:

[tex]KE=\frac{1}{2}I\omega^2[/tex]

where I is the moment of inertia, and ω is the angular velocity.

The moment of inertia is defined as:

[tex]I=MR^2[/tex]

where M is the mass and R is the distance from the axis of rotation.

In case of rod A :

the rod is massless so only the moment of inertial of the particle is considered, then

[tex]K_A=\frac{1}{2}MR^2\omega^2\\\\K_A=0.5\times0.75\times(0.87)^2\times(4.6)^2J\\\\K_A=6J[/tex]

In case of rod B:

The rod has a mass of 0.75 kg uniformly distributed and the moment of inertia of a uniform rod is given by;

[tex]I=\frac{1}{3}ML^2[/tex]

where L is the length of the rod

so,

[tex]K_B=\frac{1}{2}\times\frac{1}{3}\times0.75\times(0.87)^2\times(4.6)^2J\\\\K_B=2J[/tex]

Learn more about rotational motion:

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