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A rigid body has a moment of inertia of 1.2 kg m² about a specified axis and is initially stationary. If it is to acquire a rotational kinetic energy of 1500 J by applying a constant angular acceleration of 25 rad s⁻² about that axis, for how long should the acceleration act?

1. 4 s
2. 2 s
3. 8 s
4. 10 s

Correct answer: 2 s

Solution

KE = (1/2)I w^2 = 1500 gives w^2 = 2500, w = 50 rad/s. With alpha = 25, t = w/alpha = 50/25 = 2 s.

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