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A uniform bar has two small balls glued to its ends. The bar is 2.00 m long and has mass 4.00 kg, while the balls each have a mass of 0.500 kg and can be treated as point masses. Find the moment of inertia of this combination about each of the following axes:

a) Axis passing through the center of the bar and perpendicular to its length.
b) Axis passing through one of the ball's centers and perpendicular to the bar.
c) Axis passing through the center of the bar and parallel to its length.
d) Axis passing through one of the ball's centers and parallel to the bar.

User Adil Malik
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Final answer:

The moments of inertia for a uniform bar with balls at its ends vary with different axes: 2.00 kg·m² for the axis through the center, 4.00 kg·m² through a ball's center, 1.33 kg·m² center parallel, and for the ball center parallel, it is trivial for the mass at the axis.

Step-by-step explanation:

The moment of inertia is a measure of an object's resistance to changes in its rotation rate. When calculating the moment of inertia for a system, different axes of rotation will give different moments of inertia. For the provided system of a uniform bar with two small balls at its ends, the moments of inertia can be calculated as follows:

  • Axis through the center of the bar: Using I₁ = mR² + mR² = 2mR², we find the moment of inertia to be I₁ = 2(0.500 kg)(1.00 m)² = 2.00 kg·m².
  • Axis through one of the ball's centers: Using I₂ = m(0)² + m(2R)² = 4mR², we find it to be I₂ = 4(0.500 kg)(1.00 m)² = 4.00 kg·m².
  • Axis through the center of the bar and parallel to its length: The bar can be treated as a thin rod, so the moment of inertia is I = ML²/12. This gives us I = 4.00 kg·(2.00 m)²/12 = 1.33 kg·m².
  • Axis through one of the ball's centers and parallel to the bar: The moment of inertia for this axis is not common and has a complex derivation, but for a point mass, it is simply I = mr², where r = 0 for the axis passing through the mass itself.

These calculations illustrate how the moment of inertia depends on the axis of rotation chosen for the calculation.

User Volna
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