question_answer 45)

                  If P, Q, R are physical quantities, having different dimensions, which of the following combinations can never be a meaningful quantity?                 (a) \[(P-Q)/R\]                  (b) \[PQ-R\]                 (c) \[PQ/R\]                        (d) \[(PR-{{Q}^{2}})/R\]                 (e) \[(R+Q)/P\]                

Answer:

                  (a, e) Since P,Q and R have different dimensions, so out of these three, any two cannot be added and cannot be substracted.