Year 12s: what will be the first way you research your future options? >>

3 forces in equilibrium help?

I have been attempting to do Question 2 (attached below) and have not been able to get Y = 5N after many attempts. I have watched a YouTube video (attached below) and then tried to answer the question using their technique. My workings are also attached below, so you can identify any errors that I have made along the way.

All help will be greatly appreciated!

Question 2:

My working:

The YouTube video:
[video="youtube;LS01iOCAEyE"]http://www.youtube.com/watch?v=LS01iOCAEyE[/video]

Reply 1

Stonebridge

The first thing I spotted was that -X cos 60 and + X sin 60 don't "cancel out".

Reply 2

x0diak

That's exactly what I thought too.

I think it was that in the video's example the angle was 45, which is the rare occasion where the sine and cosine of the angle are the same.

However I do not see how I can find out Y when I do not know the value of X :frown:

Reply 3

RVNmax

Original post by x0diak

really? you missed something very big!
It's very short, fill in the missing angles i.e. between Y and X, you should notice something. :smile:

Reply 4

x0diak

I still can't get Y to equal 5 :confused:

Can you show me the full working and indicate where I went wrong please? :frown:

Reply 5

Username_valid

Original post by x0diak

I still can't get Y to equal 5 :confused:

Can you show me the full working and indicate where I went wrong please? :frown:

You've resolved it correctly, but what followed is incorrect (xsin60 is the same as xcos30 but not the same as xcos60).

Re-arrange your first line to make x the subject of the formula (make x in terms of y) (it might help to know that cos60 = 0.5). Substitute x into your second equation. Take 10 to the other side, factorise the LHS by taking out y and find y.