Question

The atwood machine shown is suspended from a spring balance. The mass on one hanger is $M$, that on other is $(M+m)$. Suppose the heavier side (right side) hanger is fastened to the top of pulley by a thread. The scale reads $(2M+m)g$. The thread is burned and the system accelerates. The reading of spring balance now will be -

• A. Same as before
• B. More than before
• C. Less than before
• D. Can’t say

Answer 1

The correct option is C Less than before

Before the burn $F_s=M_{total}g=(2M+m)g$

After the burn the situation is as shown in figure

F.B.D of whole system:
$(2M+m)g-F_s=(2M+m)a_{\text{cm}}$
$\therefore F_s<(2M+m)g$