Kinetic friction f_k is given by:
Af_k = μ_k N
Bf_k = μ_s N
Cf_k = μ_k m
Df_k = 0
Answer & Solution
Correct answer: A. f_k = μ_k N
Kinetic friction = μ_k × N, where μ_k is coefficient of kinetic friction and N is normal reaction. Unlike static friction, this is a definite value (when surfaces slide).
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