+0  
 
0
711
4
avatar+1832 

what is my mistake here? 

it is written in the solution manual that FCB is tension?? 

 

 

 

 

 

 Sep 13, 2015

Best Answer 

 #3
avatar+33603 
+5

You should have FCB = 30*sin(alpha), and since alpha = 36.27° you should end up with a positive value for FCB. (You need to resolve the 30N force parallel and perpendicular to BC - FCB is the parallel component - not resolve FCB into horizontal and vertical components.  alpha is the angle between the 30N force and the perpendicular to BC).

 

The above assumes AB exerts no force on BC and that the 30N is the only force in play.  However, if AB exerted a horizontal reaction force on BC, the net effect would still be for a tendency to stretch BC, hence for BC to be in tension.

 Sep 13, 2015
edited by Alan  Sep 13, 2015
edited by Alan  Sep 13, 2015
edited by Alan  Sep 13, 2015
 #1
avatar+33603 
+5

In your sketch you have defined the direction of FCB as positive for tension.   FCB is trying to stretch BC, so BC is in tension. 

 Sep 13, 2015
 #2
avatar+1832 
0

In my calculation I got FCB negative , so I must revesrse its direction ! so it will be compression . 

 

thats how I understand 

 Sep 13, 2015
 #3
avatar+33603 
+5
Best Answer

You should have FCB = 30*sin(alpha), and since alpha = 36.27° you should end up with a positive value for FCB. (You need to resolve the 30N force parallel and perpendicular to BC - FCB is the parallel component - not resolve FCB into horizontal and vertical components.  alpha is the angle between the 30N force and the perpendicular to BC).

 

The above assumes AB exerts no force on BC and that the 30N is the only force in play.  However, if AB exerted a horizontal reaction force on BC, the net effect would still be for a tendency to stretch BC, hence for BC to be in tension.

Alan Sep 13, 2015
edited by Alan  Sep 13, 2015
edited by Alan  Sep 13, 2015
edited by Alan  Sep 13, 2015
 #4
avatar+1832 
+5

Now I get it 

Thank you 

 Sep 14, 2015

2 Online Users