Q82 / 90 · JEE Main 2022 (27 Jun Shift 2) · Physics

A rolling wheel of 12 kg is on an inclined plane at position P and connected to a mass of 3 kg through a string of fixed length and pulley as shown in figure.
Consider PR as friction free surface.
The velocity of centre of mass of the wheel when it reaches at the bottom Q of the inclined plane PQ will be 12xgh m s-1. The value of x (rounded off to the nearest integer) is _____.

Figure

Correct answer: 3

Solution

If we take the wheel as a ring then its moment of inertia will be, I=Mr2.

Using mechanical energy conservation,

Mgh-mgh=12mv2+12Mv2+12Iω2⇒12gh-3gh=123v2+1212v2+1212r2v2r2

⇒9gh=15v2+12v22

⇒v=23gh=1283gh

Therefore, x=83≃3

Hence, the correct answer is 3.

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