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Question:

A block has been placed on an inclined plane with the slope angle θ, block slide down the plane at constant speed. The coefficient of kinetic friction is equal to:

cosθ

sinθ

secθ

tanθ

Solution:

If μ be the coefficient of kinetic friction, then the friction force f = μN
Now , normal force N = mgcosθ
so f = μmgcosθ
In equilibrium, mgsinθ = f = μmgcosθ
or μ = sinθ/cosθ = tanθ