Question

) to keep a door closed, a wooden stick is wedged between the floor and the doorknob. the stick exerts at b a 175 n force directed along line ab. replace that force with a equivalent force couple system at

c.

Answer 1

The 175 N force is in the path A to B since a stick can’t pull the doorknob, this can be written as:

(F ) ⃗= 175⋅(73i ⃗+990 j ⃗+494 k ⃗)/(√73² +990²+ 494² )
(F ) ⃗=(11.5i ⃗+156 j ⃗+78.0k ⃗ )N

The displacement form C to B is:
(r ⃗ )_(B/C)=(683 i ⃗+860 j ⃗+0k ⃗ )mm

The formula for the moment about C is
M ⃗_c= (r ⃗ )_(B/C) x (F ) ⃗
M ⃗_c= (683 i ⃗+860 j ⃗ ) x (683 i ⃗+860 j ⃗+0k ⃗ )mm.N
M ⃗_c= (67.1 i ⃗+53.3 j ⃗+116 k ⃗ )m.N