Marginal physical product of a variable input is negative

A. Only in 1^st stage

B. Only in 3^rd stage

C. Only in 2^nd stage

D. In 2^nd and 3^rd stages

Answer: Option D

Solution(By Examveda Team)

The marginal physical product (MPP) of a variable input becomes negative in the short run when the law of diminishing returns sets in. This typically occurs in the 2^nd stage and continues into the 3^rd stage. In the short run, as more of a variable input (like labor) is added to a fixed input (like land), the additional output (marginal product) may initially increase but eventually starts to decrease, leading to a negative marginal physical product. Therefore, in this context, the correct option is Option D: In 2^nd and 3^rd stages.