Practice question
Question
A plate of area 0.06m2 moves at 0.9m/s over a 0.5mm thick honey film (η\=0.2Pa s). What force is required?
Explanation
Viscous force: F = ηvAl. η = 0.2Pa s, v = 0.9m/s, A = 0.06m2, l = 0.5×10−3m. F = 0.2×0.9×0.060.5×10−3 = 0.2×108 = 21.6N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 22 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.