A ring of mass \(\mathrm{M}\) and radius \(\mathrm{r}\) is melted and then molded in to a sphere then the moment of inertia of the sphere will be..... \(\\{\mathrm{A}\\}\) more than that of the ring \\{B \\} Less than that of the ring \(\\{\mathrm{C}\\}\) Equal to that of the ring \\{D\\} None of these

Short Answer

Expert verified
The moment of inertia of the sphere is less than that of the ring. The correct answer is (B) Less than that of the ring.

Step by step solution

01

Calculate the moment of inertia of the ring

The moment of inertia of a ring with mass \(M\) and radius \(r\) is given by the formula: \(I_\text{ring} = Mr^2\) In our case, we have the mass (\(M\)) and radius (\(r\)) of the ring, so we can directly apply this formula: \(I_\text{ring} = M r^2\)
02

Calculate the moment of inertia of the sphere

When the ring is melted and molded into a sphere, its moment of inertia will be given by the formula: \(I_\text{sphere} = \frac{2}{5}M R^2\) Since the mass and radius of the sphere are both equal to the mass and radius of the ring, we can substitute those values: \(I_\text{sphere} = \frac{2}{5}M r^2\)
03

Compare the moments of inertia

Now we have both moments of inertia and can compare them: \(I_\text{ring} = M r^2\) and \(I_\text{sphere} = \frac{2}{5}M r^2\) Start by dividing both sides by \(M r^2\): \(\frac{I_\text{ring}}{M r^2} = 1\) and \(\frac{I_\text{sphere}}{M r^2} = \frac{2}{5}\) Now we compare these two ratios, noticing that \(\frac{2}{5} < 1\) This means that \(I_\text{sphere} = \frac{2}{5}M r^2 < M r^2 = I_\text{ring}\) Hence, the moment of inertia of the sphere is less than that of the ring.
04

Answer

The correct answer is (B) Less than that of the ring.

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