Along incline:
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Fnet = ma
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Fnet = m(0) (else car will accelerate down incline)
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Friction acts up incline and gravity acts down incline.
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Fnet = Ff + Fg
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==> 0 = Ff + Fg (vectors)
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Since Ff and Fg act in opposite directions, their magnitudes must be equal :
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Ff = Fg (scalars)
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or μ Fn= Fg
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==> μ mg cosθ = m g sinθ
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==> μ = tanθ
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==> θ = tan-1 (μ) = tan-1 (0.68) = 34.21 degree
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Hope this helps u!