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problem11_71

University Physics with Modern Physics with Mastering Physics (11th Edition)

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11.71: a) Consider the forces on the roof V and H are the vertical and horizontal forces each wall exerts on the roof. 2 so 2 roof. the of weight total the is N 000 20 w V w V , w = = = . length have half each Let join. halves two the where line the along axis with the roof, the of half one to 0 Apply L = Σ τ N 7140 0 35 tan 4 0 35 cos 0 35 sin 2 use and out, divides 0 0 35 cos 0 35 sin ) 35.0 cos )( 2 ( ) 2 ( 4 1 = ° = ° = ° = = ° - ° + ° . w H . w . H w V L . VL . HL L w By Newton’s 3rd law, the roof exerts a horizontal, outward force on the wall. For torque about an axis at the lower end of the wall, at the ground, this
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Unformatted text preview: force has a larger moment arm and hence larger torque the taller the walls. b) Consider the torques on one of the walls. H is the horizontal force exerted by the roof, as considered in part (a). B is the horizontal force exerted by the buttress. Now the angle is , 40 ° so N 5959 40 tan 4 = ° = w H . B ) B( ) H( N 7900 and m 30 m 40 ground at the axis , = =-= ∑ τ...
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