ch06-p020 - 20. (a) In this situation, we take f s to point...

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20. (a) In this situation, we take G f s to point uphill and to be equal to its maximum value, in which case f s , max = s N F μ applies, where s = 0.25. Applying Newton’s second law to the block of mass m = W / g = 8.2 kg, in the x and y directions, produces min 1 , max sin 0 cos 0 s N Fm g f m a g θ −+ = = −= which (with = 20°) leads to () min 1 sin cos 8.6 N. s g θμ = (b) Now we take G f s to point downhill and to be equal to its maximum value, in which case f s , max = s F N applies, where s = 0.25. Applying Newton’s second law to the block of mass m = W / g = 8.2 kg, in the x and y directions, produces min 2 , max sin 0 cos 0 s N g f m a g =− = = which (with = 20°) leads to
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