still absolutely stuck! don't seem to have enough information in the diagram, like the angle of the bottom arm etc? surely they don't want me to just guess??

o.

 

aaaaaaaargh i hate things like this that make me feel stupid! NY resolution now to attend uni when i should!

o

 

Ah, I did an Meng Hons in Mechanical myself, wasnt keen to specialise any heavier into automotive in case I got unlucky and ended up designing electric window motor arm mechanisms for a living....

Didnt have time to look at this in my lunch (didnt even get one but thats the joys of working life I guess for you!)

Running through it just now on a bit of paper I'm overcomplicating question 2 when I try and do it, so I'm not going to run you through what I did on it as to be honest I've finished my degree now, Damians done it and I cant be bothered on a Friday night!

Question 3 is incredibly simple however, I hesitate to recommend any books to look in as they'd be general mechanical industrial spring selection and sizing design formulas rather than out and automotive spring formulas, which would probably give the game away- but it really is a basic calc- everythings there given for you to plug in.

 

get my head down on it tomorrow i guess.... mate's birthday bash tonight and this has to be in on monday.... thanks for the advice guys!

Owain

 

if anyone is willing to help me out any more on this one i'd be really grateful.. it's proving more or less impossible i'm afraid.

thanks
Owain

 

owain, its a simple mechanics problem.

resolve twice take moments once.

In order to resolve you balance the forces in that direction, simplified to f=ma (no vector cross products here!

if in equilibrium, forces balance no resultant acceleration, so the sum of all forces in that direction should equal zero.

Same goes for in another direction, whichever you choose it won't matter as the sum will always be zero.

damian suggests two directions, these are normally chosen for the reason of simplifying angles or simplifying the equations by choosing directions at right angles to one another.

you choose a point to take moments about. preferably a pivot point which has a force acting through it. By doing that you can eliminate that force from the moments equation as the perpendicular distance from the pivot is zero, therefore that force is irrelevant.

Once you have done this as Damian said, you will have three equations with 4 unknown quantities. This is not enough information to solve.

Not looked at this bit, but damian says there is a relatinship you can write down, which will give you a 4th equation between the quantities you are trying to solve.

Once you have these four simultaneous equations, you can rearrange the appropriate one and substitute that into another.

Fromt hen on you will be able to work out what the unknown quantities are.

Ignore the physics here, this is all very simple A-level mechanics.

 

right i've just discovered that 2 angles are missing from the question... the angle between the strut and the lower arm is 55 degrees and the angle between the lower arm and the horizontal is 10 degress.... i've missed LOADS of lectures last term and really don't know what you guys mean by taking moments etc..

i know it's cheating but to avoid flunking this subject i really need a model answer.... if i promise to attend from now on can anyone help? please?

thanks
Owain

 

ps. didn't do a-levels got in here on my mechanical experience, but too much f***ing about last term has put me on the back foot

 

havent got time to start writing out a model answer.

But to take moments assuming equilbrium, then anti clockwise moment = clockwise moment.

Choose a pivot point. then sum of all the moments in clockwise direction minus sum of moments in anticlockwise direction = 0. That is an equation.

The Moment is given by force multiplied by perpendicular distance from the pivot point you have chosen.

I hate to say ti, but if you don't understand this, then anyone on here doing this for you is not going to help you at all.

You really need to follow through the old lectures one by one and have someone sit down with you and explain this problem so that you can see how to resolve forces.