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JEE Mains · Physics · STD 11 - System of particles and rotational motion
  • JEE Mains 2026
  • Medium
  • Numerical

A fly wheel having mass 3 kg and radius 5 m is free to rotate about a horizontal axis. A string having negligible mass is wound around the wheel and the loose end of the string is connected to a 3 kg mass. The mass is kept at rest initially and released. Kinetic energy of the wheel when the mass descends by 3 m is ___________ J. (\(g=10~m/s^{2}\))

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Answer & Solution

Correct Answer

(A) 30

Step-by-step Solution

Detailed explanation


image
\(mg\times3=\frac{1}{2}.\frac{mR^{2}}{2}\omega^{2}+\frac{1}{2}mv^{2}\) ...(i)
& \(v=\omega R\) ...(ii)
From equation (i) & (ii)
\(g\times3=\frac{3}{4}.v^{2}\)
K.E. of flywheel \(=\frac{1}{2}\times\frac{mR^{2}}{2}\times\omega^{2}=\frac{1}{4}mv^{2}\)
\(=\frac{1}{4}\times3\times40=30\) Joule
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