Explanation:
A) To prove the motion of the center of mass of the cylinders is simple harmonic:
System diagram for given situation is shown in attached Fig. 1
We can prove the motion of the center of mass of the cylinders is simple harmonic if
![a_{x} = -\omega^{2} x](https://tex.z-dn.net/?f=a_%7Bx%7D%20%3D%20-%5Comega%5E%7B2%7D%20%20x)
where aₓ is acceleration when attached cylinders move in horizontal direction:
<h3>PROOF:</h3>
rotational inertia for cylinders is given as:
-----(1)
Newton's second law for angular motion is:
∑τ = Iα ------(2)
For linear motion in horizontal direction it is:
∑Fₓ = Maₓ ------ (3)
By definition of torque:
τ = RF --------(4)
Put (4) and (1) in (2)
from Fig 3 it can be seen that fs is force by which the cylinders roll without slipping as they oscillate
So above equation becomes
------ (5)
As angular acceleration is related to linear by:
![a= R\alpha](https://tex.z-dn.net/?f=a%3D%20R%5Calpha)
Eq (5) becomes
---- (6)
aₓ shows displacement in horizontal direction
From (3)
∑Fₓ = Maₓ
Fₓ is sum of fs and restoring force that spring exerts:
----(7)
Put (7) in (3)
[/tex] -----(8)
Using (6) in (8)
![\frac{1}{2}Ma_{x} - kx =Ma_{x}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B2%7DMa_%7Bx%7D%20-%20kx%20%3DMa_%7Bx%7D)
--- (9)
For spring mass system
----- (10)
Equating (9) and (10)
![\omega = \sqrt{ \frac{2k}{3M}}](https://tex.z-dn.net/?f=%5Comega%20%3D%20%5Csqrt%7B%20%5Cfrac%7B2k%7D%7B3M%7D%7D)
then (9) becomes
![a_{x} = - \omega^{2}x](https://tex.z-dn.net/?f=a_%7Bx%7D%20%3D%20-%20%5Comega%5E%7B2%7Dx)
(The minus sign says that x and aₓ have opposite directions as shown in fig 3)
This proves that the motion of the center of mass of the cylinders is simple harmonic.
<h3 /><h3>B) Time Period</h3>
Time period is related to angular frequency as:
![T=\frac{2\pi }{\omega}](https://tex.z-dn.net/?f=T%3D%5Cfrac%7B2%5Cpi%20%7D%7B%5Comega%7D)
![T = 2\pi \sqrt{\frac{3M}{2k}](https://tex.z-dn.net/?f=T%20%3D%202%5Cpi%20%5Csqrt%7B%5Cfrac%7B3M%7D%7B2k%7D)