Tension And Inclidsd Plane

[chemia]

A massive light hangs over the table in Jeremy's dining room. The light is supported by four strong chains which make an angle of 79° with the horizontal. The force in each chain is 35.8 N.
a. Determine the force with which a single chain pulls horizontally and vertically upon the light.
b. Determine the mass of the light

[Rosetta]

many apologies chemia. Is this an exam question

[woofgang]

3 determine how to get a poster to use please and thank you when asking for help.

[factor-fiction]

Draw a diagram showing all the forces in each direction. Remember to take account of the angle- you decide which trig function to use for each.

[jomifl]

Just a hint, when you have done the trig, mutliply the answer by 4 for the mass of the loiht.

[Peter Pedant]

I am right in thinking that the chains outline a pyramid in three D
dont they or have I gone mad (again) ?

[jomifl]

PP it could be a truncated pyramid,( with 4 attachments to the ceiling) the forces should be the same unless I am your neighbour in the asylum :o)

[jomifl]

You have to ignore the catenary effect of the chain which will contribuet to the ension in the chain as you haven't been told it's weight.

[vascop]

Why don't you have a go chemia and post your answers here and we can give you our verdict?

[Peter Pedant]

PP writes: OK I have done my diagram which is a section between opposite corners of the 'pyramid' - and looks a bit like a 'Y'. Light is M kg and the known tension T is 35.8 N

R hx - T cos79 = T cos 79 - not sure about this
R Vx - I initially thought I could take a planar section but I have decided I cant,
so 4 T sin 79 = Mg where M is the mass of the light (kg)

Once I have got sin79 in degz = .981 (looks hopeful)

Then 4 . (35.8) . (0.981) /9.81 = M and M is 14.32 kg

and I have decided that the H force on a chain whose tension is 35.8 is 35.8 cos 79 or (0.2 x 35.8) or 7.16N and the vertical is force is 35.8 sin 79 or ( 35.1 N)

or is it not ?

[vascop]

Amazing how many people post questions like this one and then after somebody makes an effort to provide an answer, they never even have the courtesy to reply.

[Peter Pedant]

Is my answer right vasco ?
You were very helpful over my cubic pure math q a few years ago.

I have re-started doing maths after a years chemo interrupted getting a place on maths degree course Apr 2012.

[vascop]

Hi Peter
It looks OK to me.
Glad you are getting back into maths. Hope you are feeling better after the chemo.

[Peter Pedant]

Thanks,
Not bad
I thought I had relapsed but instead it is chronic infection - yippee it means I dont have a death sentence....(yeah its that good)