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 0.76 kg attached to its free end. Rod B has a mass of 0.76 kg, which is distributed uniformly along its length. The length of each rod is 0.88 m, and the angular speed is 5.2 rad/s. Find the kinetic energies of rod A with its attached particle and of rod B.

Respuesta :

To solve the exercise it is necessary to apply the concepts related to Kinetic Energy and its respective definition. Angular kinetic energy means that,

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

Where

I = Inertia moment

\omega = Angular velocity

On the other hand the inertia of a rod is given by

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

Where,

m = mass

l = length

ROD A: The data for Rod A is given as,

l = 0.88m

m = 0.76Kg

[tex]\omega = 5.2 rad/s[/tex]

The inertia would be

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

[tex]I = 0.76Kg*0.88^2[/tex]

[tex]I = 0.588544 kgm^2[/tex]

Therefore the Kinetic Energy would be

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

[tex]KE = \frac{1}{2} (0.588544)(5.2)^2[/tex]

[tex]KE= 4.683J[/tex]

ROD B: The data for Rod B is given as

[tex]l = 0.88m[/tex]

[tex]m = 0.76Kg[/tex]

[tex]\omega = 5.2 rad/s[/tex]

The inertia would be

[tex]I = \frac{1}{3}ml^2 \rightarrow[/tex] Note that the moment of inertia is not about its reference system, but about its end.

[tex]I = \frac{1}{3}0.76Kg*0.88^2[/tex]

[tex]I = 0.19618 kgm^2[/tex]

Therefore the Kinetic Energy would be

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

[tex]KE = \frac{1}{2} (0.19618)(5.2)^2[/tex]

[tex]KE= 2.6523J[/tex]