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NEET PHYSICSMedium

A solid cylinder of mass 50 kg50 \text{ kg} and radius 0.5 m0.5 \text{ m} is free to rotate about the horizontal axis. A massless string is wound round the cylinder with one end attached to it and other hanging freely. Tension in the string required to produce an angular acceleration of 2 rev/s22 \text{ rev/s}^2 is:

A

25 N25 \text{ N}

B

50 N50 \text{ N}

C

78.5 N78.5 \text{ N}

D

157 N157 \text{ N}

Step-by-Step Solution

Given: Mass of the cylinder, M=50 kgM = 50 \text{ kg} Radius of the cylinder, R=0.5 mR = 0.5 \text{ m} Angular acceleration, α=2 rev/s2=2×2π rad/s2=4π rad/s2\alpha = 2 \text{ rev/s}^2 = 2 \times 2\pi \text{ rad/s}^2 = 4\pi \text{ rad/s}^2

The moment of inertia of a solid cylinder about its central axis is given by: I=12MR2I = \frac{1}{2}MR^2

The torque τ\tau produced by the tension TT in the string acting at the rim of the cylinder is: τ=T×R\tau = T \times R

According to Newton's second law for rotational motion, we know that: τ=Iα\tau = I\alpha

Equating the two expressions for torque: T×R=(12MR2)αT \times R = \left(\frac{1}{2}MR^2\right)\alpha T=12MRαT = \frac{1}{2}MR\alpha

Substituting the given values into the equation: T=12×50×0.5×4πT = \frac{1}{2} \times 50 \times 0.5 \times 4\pi T=12.5×4π=50π NT = 12.5 \times 4\pi = 50\pi \text{ N}

Taking π3.14\pi \approx 3.14: T=50×3.14=157 NT = 50 \times 3.14 = 157 \text{ N}

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