Can someone please look at this problem for me, I desperately need some help. ht
ID: 1851846 • Letter: C
Question
Can someone please look at this problem for me, I desperately need some help. http://www.chegg.com/homework-help/engineering-mechanics-statics-11th-edition-chapter-4-problem-5p-solution-9780132215008 I need someone to explain step 2, this entire thing confuses me. I do not understand why some values are positive, and others are negative. For example, If you were to apply either one of these forces individually about point P, the result would be clockwise rotation, right? If that is true, why are some of the forces positive and some negative? Also, please explain why cos and sin are used where they are and why they are being multiplied (respectively) by the chosen distances. I realize this must seem basic, but I have gotten most of the stuff in the book up until now. Please break this problem down for me as if I were the simpleton that I am. Please note, I do understand where the distance values are coming from, i just dont understand why they are being multiplied by sin or cos respectively and where the positive vs negative or adding and subtracting are coming from.Explanation / Answer
(1) For each force, if the moment of that force about the point P is clockwise, then it is negative, otherwise, it is positive.
(2) IN this step, the forces are decomposed into x- and y-component and then calculate the moment
The 40 lb force:
x-component = 40 cos 45, and its moment is CCW, therefore, 40 cos 45 * (3+3) in
y component = 40 sin45, and its moment is CW, therefore, -40 sin 45 * (6+6) in
The 60 lb force:
x-component = 60 sin 30, and its moment is CW, therefore, -60 sin30 * (5-3) in
y component = 60 cos 30, and its moment is CW, therefore, -60 cos30 * (12+6) in