- #1
Qube
Gold Member
- 468
- 1
- Homework Statement
- Draw a free-body diagram for the top truck. Image below.
- Relevant Equations
- sum of forces in x-direction = 0
sum of forces in y-direction = 0
sum of moments = 0
Problem statement:
Attempt at a solution:
1) There are no relevant moments that need to be drawn in this free-body diagram.
2) There is tension in the chain DE that is pointed away from the truck, i.e. from D to E.
3) There are "ground" reaction forces at points A and B pointed up toward the truck.
4) There is an arrow starting from G and pointing away from the truck; this arrow represents the Fw, or the weight of the truck.
Question:
Should one include frictional forces at points A and B when drawing the FBD?
The question is vague enough that I think that not including frictional forces at contact patches A and B would not represent a failure of understanding. There's no indication that there's actually any tension in the chain, i.e. the tension in the chain could very well be 0.
On the other hand, I think that a 100% complete solution would include arrows that are perpendicular to the ground reaction forces at A and B pointed toward the "right," or opposite that of the sense of the chain tension.
The end-of-book answer key does not include friction in the FBD. Would including friction make the FBD incorrect in any way?
Attempt at a solution:
1) There are no relevant moments that need to be drawn in this free-body diagram.
2) There is tension in the chain DE that is pointed away from the truck, i.e. from D to E.
3) There are "ground" reaction forces at points A and B pointed up toward the truck.
4) There is an arrow starting from G and pointing away from the truck; this arrow represents the Fw, or the weight of the truck.
Question:
Should one include frictional forces at points A and B when drawing the FBD?
The question is vague enough that I think that not including frictional forces at contact patches A and B would not represent a failure of understanding. There's no indication that there's actually any tension in the chain, i.e. the tension in the chain could very well be 0.
On the other hand, I think that a 100% complete solution would include arrows that are perpendicular to the ground reaction forces at A and B pointed toward the "right," or opposite that of the sense of the chain tension.
The end-of-book answer key does not include friction in the FBD. Would including friction make the FBD incorrect in any way?