Question

Two identical blocks of mass $M$ are linked by a thread wrapped around a pulley-block with a fixed axis. A small block of mass $m$ is placed on one of the blocks as shown. If pulley and strings are ideal, the force exerted by small block $m$ on block $M$ is

• A. $\frac{mMg}{2M+m}$
• B. $\frac{2mMg}{2M+m}$
• C. $\frac{2mMg}{M+m}$
• D. $\frac{2m^{2}g}{2M+m}$

Answer 1

The correct option is B $\frac{2mMg}{2M+m}$

Acceleration of the system,

$a=\frac{mg}{2M+m}$

$\therefore$ Force on M by m,

$F=m(g-a)=m(g-\frac{mg}{2M+m})F=\frac{2Mmg}{2M+m}$