A uniform disc of radius R and mass M is free to oscillate about the axis A as shown in the figure. For small oscillations the time period is . (g is acceleration due to gravity) [figure]
- 2 5R4g
- 2 2R3g
- 2 3R2g
- 2 3Rg
Answer
(1) 2 5R4g
Solution
Axis A is a tangent to the disc lying in the plane of the disc.
[figure]
About a diameter: Id= MR24
Parallel-axis theorem (axis A is at distance R from the diameter):
IA= MR24+MR2= 54MR2
Physical pendulum with the centre of mass at d=R from the axis:
T=2 IAMgd=2 54MR2MgR
T=2 5R4g
Answer: (1)