# Why the weight force is not included in this free-body diagram

Take a look at this question. The solution by the author is My question is why the weight force is ignored in the free-body diagram? Is it because the roller(A) and the pint(B) which cancel the effect of the gravitational force?

• It must be that the weight of the member is assumed to be negligible. – Bob D Sep 19 '19 at 21:22
• @BobD, that actually possible. Unfortunately, nothing stated in the question. Also, this chapter talks about free-body diagram so I've assumed I have to include all forces acting on the body. – CroCo Sep 19 '19 at 21:25
• Since it wasn't stated you need to assume so. You assume correctly. A FBD must include all forces, including weight. You can't determine reactions at the pin and roller otherwise. The roller and pin vertical reaction must equal the weight as well as the vertical component of the 390 lb force. – Bob D Sep 19 '19 at 21:31
• Where did the 390 lb come from? I would take the y-component of that as the weight. And, therefore, the weight is used. – jmh Sep 19 '19 at 21:36
• @jmh, well, may be an external force who knows except the author. But it seems the question is not very well written. Also, if this is the weight vector, why it is not drawn as an vertical downward vector?! I will go with BobD since the mass of the body is not mentioned. – CroCo Sep 19 '19 at 21:37