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Question: Answered & Verified by Expert
A highly rigid cubical block A of small mass M and side L is fixed rigidly on to another cubical block B of the same dimensions and of low modulus of rigidity η such that the lower face of A completely covers the upper face of B. The lower face of B is rigidly held on a horizontal surface. A small force F is applied perpendicular to one of the side faces of A. After the force is withdrawn, block A executes small oscillations, the time period of which is given by 
PhysicsOscillationsJEE Main
Options:
  • A 2πMηL
  • B 2πMηL
  • C 2πMLη
  • D 2πMηL
Solution:
2142 Upvotes Verified Answer
The correct answer is: 2πMηL
Modulus of rigidity, η= F A.θ Here, A= L 2

And

θ = x L
 
Therefore, restoring force is F=ηAθ=ηLx


 
Or acceleration, a= F M = ηL M x

Since, ax , oscillations are simaple harmonic in nature, time period of which is given by

T=2π | displacement acceleration | =2π | x a | =2π M ηL

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