Physics question.

I assume that the rod is in equilibrium?
First calculate all of the anticlockwise moments (i.e. the weights to the left of the pivot)
Here we have 3N which is 45cm from the pivot and 2N which is 25cm from the pivot.
The total anticlockwise moment is the sum of the two products.

Then the clockwise moments are WN 30cm from the pivot.

Now because the rod is in equilibrium the sum of all of the moments is zero. In other words, total anticlockwise moment = total clockwise moment. Using that you can rearrange for W.

If you haven't got this in mind already, ALWAYS draw a diagram for mechanics questions.

Thanks you very much But I'm abit stupid and don't really understand how you worked out the relative distance from the Pivot ?:s Can you please explain that?

It's a metre rule (says in the question) and it says it hung from the centre of mass (for a uniform rod, this is the centre of the rod - it doesn't say it's a non-uniform rod, so we assume it is uniform)
The centre of a metre rule is at the 50cm mark, so that's where the pivot is, then you work out how far away 5cm, 25cm and 80cm are from the 50cm point.

If you draw a diagram, everything becomes so much simpler!

I did draw a diagram but I just didn't really know what a metre rule was I thought it's just like a ruler and I did at some point ask myself if i need to know how long the thing was Why do always mess up at stupid little things like that.

P.S: I've got abit of language problem cause i havent been in the UK that long that's why i didn't know what a metre rule is..still common sense but I dont know)

Ah ok!
I did a quick diagram to show you the sort of thing that you might want to do.
But it's better to do it in pencil, don't do it with a Sharpie like I did:

Thanks so much for all the helping I appreciate that....if only my teachers were that helpful:') Are you doing ALevel Physics ? If you do is it really as hard as everyone keeps telling me?:s

Ah ok!
I did a quick diagram to show you the sort of thing that you might want to do.
But it's better to do it in pencil, don't do it with a Sharpie like I did:

Skills!

WRT 'hardness' of the A level - seems to come more naturally to some people than others

Ah ok!
I did a quick diagram to show you the sort of thing that you might want to do.
But it's better to do it in pencil, don't do it with a Sharpie like I did:

Draw out like this, but the weight at 25cm is 2N not 25N. Accept the fact that the sum of the anti-clockwise moments about the pivot (at 50 cm) = the sum of the clockwise moments about the pivot.

Thus: 0.3m*W = 0.25m*2N + 0.48m*5N. Some mental arithmetic gives me 29/3. However, it's pretty late so don't take my word for it!

Oh yeah! Sorry, my bad - I guess I wrote the 2 and had "25" on my mind!

Draw out like this, but the weight at 25cm is 2N not 25N. Accept the fact that the sum of the anti-clockwise moments about the pivot (at 50 cm) = the sum of the clockwise moments about the pivot.

Thus: 0.3m*W = 0.25m*2N + 0.48m*5N. Some mental arithmetic gives me 29/3. However, it's pretty late so don't take my word for it!

What exactly did you think a metre rule was?

Everyone makes mistakes :P

Nope you've done something wrong cause I got the answers in my book and manitude had the right answer(6.2N) Thanks though And @manitude I guess im good at maths i just keep making those stupid little mistakes whenever I do any question....but not only maths. Guess im gonna have to check myslef for dyslexia or something :s