Blocks A and B have masses 3m and m, joined by a massless string; the system hangs from a vertical spring as shown. Immediately after the string between them is cut, find magnitudes of accelerations of A and B.

Question

G1 Physics · Accepted Answer

Before cutting, the spring balances total weight 4mg. Immediately after cutting, its extension and upward spring force remain 4mg. On A (3m), net upward force=4mg-3mg=mg, so aₐ=g/3 upward. Block B falls freely with acceleration g. Answer: B.