question_answer

Two blocks A and B of masses 3m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of A and B immediately after the string is cut, are respectively                                                                   

A)  \[\frac{g}{3},\frac{g}{3}\]                           

B) \[g,\frac{g}{3}\]

C)  \[\frac{g}{3},g\]              

D)  \[g,g\]

Correct Answer: C

Solution :

                Sol.                       Before the string is cut \[kx=T+3mg\]                                    ?(i) \[T=mx\]                                                             ?(ii) \[\Rightarrow \]               \[kx=4mg\] After the string is cut, T = 0 \[a=\frac{kx-3mg}{3m}\] \[a=\frac{4mg-3mg}{3m}\] \[a=\frac{g}{3}\uparrow \]