Practice question
Question
A plate of area 0.06m2 moves at 0.6m/s over a 0.4mm thick glycerine film (η\=0.83Pa s). What force is required?
Explanation
Viscous force: F = ηvAl. η = 0.83Pa s, v = 0.6m/s, A = 0.06m2, l = 0.4×10−3m. F = 0.83×0.6×0.060.4×10−3 = 0.83×90 = 74.7N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 74.7 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.