Meriam, Kraige & Bolton — Equilibrium of Rigid Bodies: Problem 4_101

⚡ Mecademy AIENG정역학 · ch4  Problem Statement The device shown is used to drag loaded wooden pallets across warehouse floors. The wood board shown is one of several members that comprise the base of the pallet. For the 4-kN force applied by a forklift, determine the magnitude of the force supported by pin C and the normal gripping forces at A and B. Problem 4/101 (a) Normal gripping forces at A and B 1. Formula: By considering the symmetry of the device and the equilibrium of one jaw member (e.g., member which forms the upper jaw), we can use the sum of moments about pivot to find the normal force . Let the pivot point be the origin . Based on the given dimensions, the positions of the key points are: Pin : Contact point (top): The external horizontal force is to the left. By symmetry, each link ( and ) carries half of the horizontal load, so the horizontal component of the force in link on pin is to the left. The vertical component is found from geometry: upward. The friction force at contact is to the right (to counter the pull). The normal force is upward on the jaw. 2. Substitution: 3. Calculation: BEC CN M = ∑ C 0 C(0,0) E(−93 mm,−55.5 mm) A(156 mm,18 mm) P=4 kNDF EF EFEF = Ex 2 kN F = Ey F = Ex ( 93 55.5 ) 2 kN ( 93 111/2 ) AF = Ax 2 kNN A M = ∑ C [x F − EEy yF ]+ EEx [x N − AA y F ]= AAx 0 [(−93)(2⋅ )− 93 55.5 (−55.5)(−2)]+[(156)(N )− A (18)(2)]=0 Moment from link at : (Clockwise) Moment from friction at : (Clockwise) Moment from normal force at : (Counter-clockwise) E