Question

Two blocks are connected by a spring. The combination is suspended, at rest, from a string attatched to the ceiling, as shown in the figure. The string breaks suddenly.

Immediately after the string breaks, what is the initial downward acceleration of the upper block of mass 2m ?

(A) 0 

(B) 3g/2 

(C) g 

(D) 2g

Answer 1

Correct option: (B) 3g/2

Explanation:

Step-I : Discuss the problem be fore cutting the string :

From force diagram of lower block,

kx₀ = mg

From force diagram of upper block :

T = 2mg + kx₀

Step-II :Discuss the problem after cutting the string.

2mg + kx₀ = 2ma

or 2mg + mg = 2ma

or 3mg = 2ma