Practice question
Question
A plate of area 0.07m2 moves at 0.6m/s over a 0.9mm thick machine oil film (η\=0.113Pa s). What force is required?
Explanation
Viscous force: F = ηvAl. η = 0.113Pa s, v = 0.6m/s, A = 0.07m2, l = 0.9×10−3m. F = 0.113×0.6×0.070.9×10−3 = 0.113×46.67 = 5.27N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.3 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.
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