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Answers
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Answer:
Option "4" Is Al Right!!
Explanation:
Given:
A solid cylinder of mass 2 kg and radius 4 cm rotating about its axis at the rate of 3 rpm. The torque required to stop after 2π revolutions is
(1) 2 × 10–6 N m
(2) 2 × 10–3 N m
(3) 12 × 10–4 N m
(4) 2 × 106 N m
Solution:
Mass of solid cylinder , m = 2kg
Radius of cylinder , R = 4cm = 0.04m
A solid cylinder is rotating about its axis,
So, momentof inertia, I = 1/2 mr²
= 1/2 × 2 × (0.04)² = 16 × 10^-4 Kgm²
= 1.6 × 10^-3 kgm²
Angular frequency, = 3rpm = 3 × 2π/60 rad/s = π/10 rad/s
Angular displacement = 2π revolution
= 2π × 2π = 4π² [ as 1 revolution = 2π ]
From conservation of energytheorem,
Change in rotational kinetic energy = torque × angular displacement
Or, 1/2 I = torque × 4π²
Or, 1/2 × 1.6 × 10^-3 × 1/100 = torque × 4
Torque = 2 × 10^-6 Nm
Hence = 2×10^-6Nm
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The Answer is option is "4" = 2*10^-6 Nm