Q 11-04-172JEE MainJEE Main 2021 (26 Feb, Shift 2)Easy
Two masses $A$ and $B$, each of mass $M$ are fixed together by a massless spring. A force acts on the mass $B$ as shown in figure. If the mass $A$ starts moving away from mass $B$ with acceleration $a$, then the acceleration of mass $B$ will be:
Answer: (D) $\frac{F-Ma}{M}$
Only the spring acts on $A$, so the spring force is $Ma$ (the spring is stretched, pulling $A$ towards $B$ and $B$ towards $A$).
On $B$: force $F$ away from $A$ and spring force $Ma$ towards $A$.
$$a_B = \frac{F - Ma}{M}$$
Solution by Sreeraj P, M.Sc Physics