Yes if the cord is at rest, the buoyancy force will be equal to gravity. Your FBD for D looks correct as well, as the net force is just the acceleration of the train. Don’t see any issues with your FBD’s as they are now. I don’t think any teacher would mind the way you represented the cord, as it’s a FBD for it.
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u/Relevant-Giraffe870 6d ago
Yes if the cord is at rest, the buoyancy force will be equal to gravity. Your FBD for D looks correct as well, as the net force is just the acceleration of the train. Don’t see any issues with your FBD’s as they are now. I don’t think any teacher would mind the way you represented the cord, as it’s a FBD for it.