# M2 help - reaction forcesWatch

#1
A smooth horizontal rail is fixed at height 3m above the ground. A uniform rod AB of length 6m is placed in a vertical plane perpendicular to the rail with the end A resting on the ground. The distance AC = 5m where C is the point of contact between the rail and the rod.

This isn't the full question obviously, but my question concerns just the information I've given here. At point C, in which direction is the reaction force? Is it perpendicular to the rod or is it in the direction of the rail?

Thanks
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9 years ago
#2
Perpendicular to rod = direction of the rail = direction in which the force acts.
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#3
The rod is slanted. It rests on the ground at point A, and also on the rail at point C. Say the point vertically below C is O, then AOC is a triangle.

So perpendicular to the rod isn't equal to the direction of the rail. Maybe I didn't word the question well at start.
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#4
I've worked out the question assuming the force acts perpendicular to the rod and came out with the right answer, so I think that's it. Thanks
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9 years ago
#5
Well, you said "A uniform rod AB of length 6m is placed in a vertical plane perpendicular to the rail"...

But if you're changing the question, I'm actually not sure, sorry.

*Edit*

Looks like you've sorted it out though.
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#6
Yeah I have thanks though. I think by vertical plane perpendicular to the rail, it doesn't mean the rod is perpendicular, but the plane that it is in. I.e. in a three dimensional perspective, rotating the whole thing 90 degrees towards you, the rod and rail would be in line.
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