Calculate Acceleration ($a$): Since the surface is frictionless, apply Newton's Second Law ($F = ma$) to the whole system: $P = (M + m)a$ $a = \frac{P}{M + m}$

Calculate Force on the Block: The force exerted by the rope on the block ($F_{block}$) is the tension at the junction between the rope and the block. This force is responsible for accelerating the block of mass $M$. $F_{block} = M \times a$ Substitute the value of $a$: $F_{block} = M \left( \frac{P}{M + m} \right)$ $F_{block} = \frac{PM}{M + m}$ (Reference: NCERT Class 11, Physics Part I, Chapter 5: Laws of Motion, Section 5.10 'Problems in Mechanics' - treating connected bodies).