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Rotation and oscillations
5 ECAT Physics questions with answers and explanations.
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What is the moment of inertia of a uniform solid disc of mass M and radius R about its central axis?
- 1 MR^2
- 2 MR^2 / 2
- 3 2MR^2 / 5
- 4 MR^2 / 3
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Correct answer: MR^2 / 2
For a solid disc about its axis, I = 1/2 MR^2.
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A simple pendulum is 2.5 m long. What is its period? (g = 10 m/s2; take pi = 3.14)
- 1 1.57 s
- 2 3.14 s
- 3 6.28 s
- 4 0.5 s
Show answer
Correct answer: 3.14 s
T = 2 pi sqrt(L / g) = 2 x 3.14 x sqrt(0.25) = 2 x 3.14 x 0.5 = 3.14 s.
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A wheel has a moment of inertia of 0.5 kg m2 and spins at 4 rad/s. What is its angular momentum?
- 1 2 kg m2/s
- 2 8 kg m2/s
- 3 0.5 kg m2/s
- 4 16 kg m2/s
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A 2 kg ball moves in a circle of radius 1.5 m at a constant speed of 3 m/s. What centripetal force acts on it?
- 1 6 N
- 2 9 N
- 3 12 N
- 4 18 N
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Resonance occurs when the driving frequency is:
- 1 Much larger than the natural frequency
- 2 Equal to the natural frequency
- 3 Zero
- 4 Half the natural frequency
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Correct answer: Equal to the natural frequency
When the driving frequency matches the natural frequency, energy is transferred most efficiently and the amplitude is largest.