Q 11-04-020JEE MainAIEEE 2007Easy
Two blocks of masses $m$ and $M$ are placed on a horizontal frictionless table and connected by a light spring. Mass $M$ is pulled to the right with a force $F$. If the acceleration of mass $m$ is $a$, then the acceleration of mass $M$ will be
Answer: (A) $\dfrac{F - ma}{M}$
The only horizontal force on $m$ is the spring force, so the spring force is $ma$.
On $M$, the applied force $F$ acts forward and the spring pulls it back with $ma$:
$$F - ma = Ma' \;\Rightarrow\; a' = \frac{F - ma}{M}$$
Solution by Sreeraj P, M.Sc Physics