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# OCR Depth in Physics Question 1 watch

1. (Original post by ombtom)
Extend the arrow for weight until it passes through the arrow for tension.

You know that the reaction force must pass through the point where the rod meets the wall.

+ That's a good attitude to have.

So the blue line is the one I need to draw.
Attached Images

2. (Original post by nwmyname)
So the blue line is the one I need to draw.
Yes, that looks right!
3. (Original post by ombtom)
Yes, that looks right!
Great! Sorted!
ooh.
Can I ask why the arrow is in that direction? Just as a theory question that I'm interesting in knowing?
4. (Original post by nwmyname)
Great! Sorted!
ooh.
Can I ask why the arrow is in that direction? Just as a theory question that I'm interesting in knowing?
To make equilibrium. Your diagram with the red and blue arrows is actually great for visualising this; the blue arrow is equal and opposite to the resultant of the red arrows.

Think about a triangle of the forces, where tails are joined to heads of the arrows. The reaction force has to be in that direction to ensure that the triangle works.
5. (Original post by ombtom)
To make equilibrium. Your diagram with the red and blue arrows is actually great for visualising this; the blue arrow is equal and opposite to the resultant of the red arrows.

Think about a triangle of the forces, where tails are joined to heads of the arrows. The reaction force has to be in that direction to ensure that the triangle works.
So simply by extending the line of weight we have made it easier to draw the blue arrow and therefore create the triangle of equilibrium?
6. (Original post by nwmyname)
So simply by extending the line of weight we have made it easier to draw the blue arrow and therefore create the triangle of equilibrium?
I think so.
7. (Original post by nwmyname)
Hi,
This question attached is really confusing me.
Why on earth is the vertical force exerted by the rod 60N??
It is really confusing me?
And the tension question too??
I've tried it but not got to either conclusions correctly!
Thanks.

Update I have got part b but part a is the one I do not understand.

8. (Original post by langlitz)

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