15. what is the resultant moment about point a of the three forces acting on the beam in the examination figure? a. 70 ft-lb clockwise b. 50 ft-lb counterclockwise c. 50 ft-lb clockwise d. 70 ft-lb counterclockwise

option B. 50 ft-lb counterclockwise

Explanation:

1) Formula: angular momentum = force × distance

2) Force 70 lb on the left side

angular momentum = 70 lb × 5' counterclokwise

3) Force 100 lb on the left side

angular momentum = 100 lb × 3' counterclockwise

4) Force 100 lb on the rigth side

angular momentum = 100 lb × 6' clockwise

5) Net angular momentum:

70 lb × 5' counterclokwise + 100 lb × 3' counterclockwise - 100 lb × 6' clockwise =

= 350 lf-ft + 300 lb-ft - 600 lf-ft = 50 lb-ft counterclockwise

Hey hope you get the answer but i suck at math sorry : (