Practice question
Question
A plate of area 0.09m2 moves at 0.5m/s over a 0.6mm thick machine oil film (η\=0.113Pa s). What force is required?
Explanation
Viscous force: F = ηvAl. η = 0.113Pa s, v = 0.5m/s, A = 0.09m2, l = 0.6×10−3m. F = 0.113×0.5×0.090.6×10−3 = 0.113×75 = 8.475N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 8.5 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.