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edexcel M2 reaction forces

Hi,

I've attached a diagram that I have to work with for a question. The line AB is a uniform rod with weight 15N, length 60cm, and is freely suspended from A. The line CB is a light inextensible string, length 80cm.

I know there will be a reaction force at A, but I can't picture what direction it should be in. Would it be perpendicular to AC? If so why? I just can't wrap my head around what reaction forces really are and why they're there. :confused:

Thank you :biggrin:

p.s. Sorry that the picture's a bit fuzzy and is sideways, I can take another picture if it's not clear enough :smile:
(edited 10 years ago)
M2-reaction-at-A.jpg167.0KB
Original post by so it goes

I know there will be a reaction force at A, but I can't picture what direction it should be in. Would it be perpendicular to AC? If so why? I just can't wrap my head around what reaction forces really are and why they're there. :confused:


If it was perpendicular to AC it would just have a vertical component, and no horizontal one.

Consider resolving horizontally for the rod. Clearly, there must be a horizontal component at A.

And if you take moments about B for the rod, the reaction at A must clearly be anticlockwise to the line BA.

So, the direction of the reaction must be somewhere between the line BA extended, and the upwards vertical.
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so it goes
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Original post by ghostwalker

So, the direction of the reaction must be somewhere between the line BA extended, and the upwards vertical.


Ahh right, thank you :biggrin:

I've never really known what reaction forces were or how I figured out what direction they were in but that makes sense :smile:

Thank you!

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