A puck rests on a horizontal frictionless plane. A string is wound around the puck and pulled on with constant force. What fraction of the disk's total kinetic energy is due to the rotation? KErot/KEtot

Respuesta :

Answer:

Explanation:

Let v be the linear velocity ,  ω be the angular velocity  and I be the moment of inertia of the the puck.

Kinetic energy ( linear ) = 1/2 mv²

Rotational kinetic energy = 1/2 I ω²

I = 1/2 m r² ( m and r be the mass and radius of the puck )

Rotational kinetic energy = 1/2 x1/2 m r² ω²

= 1/4 m v² ( v = r ω )

Total energy

= Kinetic energy ( linear ) + Rotational kinetic energy

= 1/2 mv² +  1/4 m v²

= 3/4 mv²

rotational K E / Total K E = 1/4 m v² / 3/4 mv²

= 1 /3

So  1 /3  rd of total energy is rotational K E.

The fraction of the disk's total kinetic energy due to the rotation is 1.

The linear kinetic energy of the disk is calculated as follows;

K.E = ¹/₂mv²

where;

  • m is the mass of the disk
  • v is the linear speed of the disk

The initial linear speed of the disk = 0 (it was initially at rest)

The initial kinetic energy of the disk;

K.E[tex]_i[/tex] = 0

The final kinetic energy of the disk is rotational kinetic energy due to its angular speed;

[tex]K.E_{rot} = \frac{1}{2} I \omega ^2[/tex]

The total kinetic energy is calculated as follows;

[tex]K_{tot} = K.E_i + K.E_{rot}\\\\K.E_{tot} = 0 + K.E_{rot}\\\\K.E_{tot} = K.E_{rot}[/tex]

The fraction of the disk's total kinetic energy due to the rotation is calculated as follows;

[tex]\frac{K.E_{rot}}{K.E_{tot}} = \frac{K.E_{rot}}{K.E_{rot}} = 1[/tex]

Thus, the fraction of the disk's total kinetic energy due to the rotation is 1.

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