PPIInfo_fl_corner-FEIM2-PP08Statics

PPIInfo_fl_corner-FE - STATICS PRACTICE PROBLEMS 1 All joints in the truss shown connect pinned axial members Determine the force in member BD Take

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Copyright 2001 Professional Publications, Inc. Statics Practice Problems - 1 STATICS PRACTICE PROBLEMS 1. All joints in the truss shown connect pinned axial members. Determine the force in member BD. (A) 250 N (Compression) (B) 250 N (Tension) (C) 450 N (Tension) (D) 600 N (Compression) Solution Take the moments about point C. () ( ) ( ) ( ) CA v 400 N 3 m 6 m 600 N 4 m 0 MR −+ = Solve for Av R , the vertical reaction at point A. Av 600 N R = Use the method of sections. Cut the truss at members BC, BD, and AD. Treat the force in member BD as an external force. Take the moments about point D.
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Copyright 2001 Professional Publications, Inc. Statics Practice Problems - 2 () ( ) ( ) ( ) D 400 N 3 m 600 N 6 m 4 m BC 0 M =−− = BC 600 N (Compression) =− Take the moments about point B. ( ) ( ) B 600 N 3 m 4 m AD 0 M + = AD 450 N (Tension) = Take the sum of the forces. BC+AD+BD 600 N 450 N BD 0 xx x F == + + = BD 150 N (Tension) x = Av Load BD 600 N 400 N BD 0 yy y FR = = BD 200 N (Tension) y = Use the Pythagorean theorem. ( ) 22 BD 150 N 200 N 250 N =+ = Answer is (B). 2 . A 4 m ladder having a mass of 18 kg is placed against a wall as shown. The coefficient of friction, m , between the ladder and the wall is 0.20. When an 80 kg painter reaches a point 2.5 m from the lower end at A, the ladder begins to slip. Determine the friction coefficient between the ladder and the floor. ;;;; ;;;; ;;;; ;;;; ;;;; ;;;; ;;;; °
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Copyright 2001 Professional Publications, Inc. Statics Practice Problems - 3 (A)0.30 (B) 0.31 (C) 0.33 (D)0.35 Solution ° µ Calculate the gravitational forces corresponding to the masses. () 2 m 18 kg 9.81 176.6 N s ⎛⎞ = ⎜⎟ ⎝⎠ 2 m 80 kg 9.81 784.8 N s = Take the sum of the moments about point A. ( ) ( ) ( ) ( ) A B B 176.6 N 2 m sin30 784.8 N 2.5 m sin30 4 m cos30 0.2 4 m sin30 0 MN N + ° ° −° = B 299.6 N N = Sum the forces in the y -direction. ( ) AA 176.6 N-784.8 N 0.2 299.6 N 0 FN =− + =
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Copyright 2001 Professional Publications, Inc. Statics Practice Problems - 4 A 901.5 N N = Sum the forces in the x -direction. AB 0 x FN N µ =− = 299.6 N 0.33 901.5 N == Answer is (C). 3. The crate shown has a mass of 20 kg and is resting on a 30 ° incline. The coefficient of static friction between the crate and the incline is 0.35. What is the minimum force P that will push the crate up the plane?
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PPIInfo_fl_corner-FE - STATICS PRACTICE PROBLEMS 1 All joints in the truss shown connect pinned axial members Determine the force in member BD Take

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