Anyone good at Mechanics/Physics? Urgent Help Required!

[dpbird90]

So, its exam resit revision time for me, need to redo Applied Structural Mechanics as part of my engineering course. Going through the past papers (our uni largely uses the same questions each year just with different numbers) one of my weaker points is equilibrium. The past paper I'm looking at shows the following question:



I cannot for the life of me remember how to do it, and google searches seem very unproductive (most give results for equilibrium in chemistry). So if there's anyone who knows how to do it, I'd be very appreciative if you could show me. Many thanks!

Also, I may need more help on other questions later on, if I do I'll post them up!

[Alfanatic]

Use trig to break each of the known forces into vertical and horizontal components. Add all the vertical ones up. Make the vertical component of the unknown forces equal to the result. Repeat for horizontal forces.

That's the best I can offer... it's been 18 years since I did this crap so I can't remember what trig to use.

EDITED because I didn't look at the chart properly. The vertical and horizontal forces don't need to be combined into a single result.

Edited by Alfanatic on Friday 23 July 13:56

[AlexB]

From memory you need to resolve all forces into their H and V components using trig.

For example -> the 8kN force at 30 degrees to the horizontal resolves to:
In the V direction the force is 8kN * sin (30 degrees) = 4 kN down
In the H direction the force is 8kN *cos (30 degrees) = 6.93 kN to the right

So if this was the only force acting then you would need H to be 6.93 kN to the left and V to be 4 kN up. As it is not the only force you need to resolve all the different forces into the V and H directions then add them together (remebering that some will reduce the overall force in a direction due to opposing directions of action)

Hope that helps (and is correct!)

[onomatopoeia]

It is 25 years since I did my maths O level (which is what it looks like the question is from?) and I didn't do anything involving forces or angles at university or since, so I don't remember any of it. My random guesses to two decimal places are H=8.16 and V=-5.45.

11 cos 25 = 9.96
15 cos 70 = 5.13
-8 cos 30 = -6.93
total 8.16


11 sin 25 = 4.65
-15 sin 70 = -14.10
8 sin 30 = 4
total -5.45

Quite happy to be shot down in flames on this one

[Alfanatic]

this might help with the trig bit.



If you equate one of the known forces to z, you can use the formulas in that to work out the x and y (vertical and horizontal components).

Edited by Alfanatic on Friday 23 July 14:04

[RobM77]

I'm really not trying to sound big or clever here, and this is a genuine query, but is this really a University question?! I'm shocked! Maybe my memory is fuzzy (I left Uni 11 years ago), but isn't this one of the easiest questions from a GCSE Physics paper? Don't you learn basic trigonometry at the start of secondary school, and this is one of the ways you learn to use it in Physics?

[kazste]

Not meant ad an insult bit Feck me you must be old to of done that in gcse. My gcse math was add this up and can you divide that (im 30) half way through hnC engineering and completely unprepared after what school taught me years ago with regards to the math I am having to do.

Edited by kazste on Friday 23 July 14:10

[onomatopoeia]

kazste said:

Not meant ad an insult bit Feck me you must be old to of done that in gcse. My gcse math was add this up and can you divide that (im 30) half way through hnC engineering and completely unprepared after what school taught me years ago with regards to the math I am having to do.

Edited by kazste on Friday 23 July 14:10

You did no trig at GCSE?

[Lucas CAV]

RobM77 said:

I'm really not trying to sound big or clever here, and this is a genuine query, but is this really a University question?! I'm shocked! Maybe my memory is fuzzy (I left Uni 11 years ago), but isn't this one of the easiest questions from a GCSE Physics paper? Don't you learn basic trigonometry at the start of secondary school, and this is one of the ways you learn to use it in Physics?

I was in the first GCSE cohort ( i think) - this was not in GCSE Physics then.

A quick Google suggests that this is fairly basic AS (lower 6th) Physics today

[crofty1984]

Alfanatic said:

Use trig to break each of the known forces into vertical and horizontal components. Add all the vertical ones up. Make the vertical component of the unknown forces equal to the result. Repeat for horizontal forces.

That's the best I can offer... it's been 18 years since I did this crap so I can't remember what trig to use.

EDITED because I didn't look at the chart properly. The vertical and horizontal forces don't need to be combined into a single result.

Edited by Alfanatic on Friday 23 July 13:56

That's the one.
Bit of SOH CAH TOA to work out the vertical and horizontal components. Add them all up and whatever you need to get them back to zero is your answer.
And robert's brother fked your mum.

[WorAl]

RobM77 said:

I'm really not trying to sound big or clever here, and this is a genuine query, but is this really a University question?! I'm shocked! Maybe my memory is fuzzy (I left Uni 11 years ago), but isn't this one of the easiest questions from a GCSE Physics paper? Don't you learn basic trigonometry at the start of secondary school, and this is one of the ways you learn to use it in Physics?

Agreed, I done this at GCSE level also. ETA I'm 26

Anyway, yes, work out the forces in the horizontal and vertical plains using Trigonometry then sum them to equal 0 (zero)

Just in case you forget, one thing my teacher taught me was if you are workig out a force/length/whatever you use cos if going across the angle. See pic. It's always stayed in my head. cos = across.



Yes I know, fail on the spelling

Edit2 because of stty drawing

Edit3 still crap but you get the picture (I hope) if not I'll do it again.

Edited by WorAl on Friday 23 July 14:29

[dpbird90]

Fantastic guys, many thanks. Yes, it is a first year University question, probably covered in A Level Physics but I didn't do physics, I was intending to do chemistry but when it came to making uni choices engineering and maths seemed much more appealing.

[Lucas CAV]

dpbird90 said:

Fantastic guys, many thanks. Yes, it is a first year University question, probably covered in A Level Physics but I didn't do physics, I was intending to do chemistry but when it came to making uni choices engineering and maths seemed much more appealing.

Your're going to have fun doing Engineering at university with no Physics A level...

Good luck!

[RobM77]

kazste said:

Not meant ad an insult bit Feck me you must be old to of done that in gcse. My gcse math was add this up and can you divide that (im 30) half way through hnC engineering and completely unprepared after what school taught me years ago with regards to the math I am having to do.

Edited by kazste on Friday 23 July 14:10

As I say, maybe my memory's bad! I'm 33 and took my GCSEs (plus an AS in Maths and something called "Additional Maths") in 1994, A Levels in 1996 and graduated from Uni in 1999. Trigonometry and the applications of it were done very early on at GCSE level, I think... I did do GCSE Maths a year early and then AS Maths and GCSE Additional Maths straight after, so maybe I'm getting confused, and I did it at school, but actually in the AS syllabus?

Even if this isn't GCSE Maths though, surely it's obvious that if you push something square on with a force of 10N then it feels a force of 10N, but if you push at an angle, the object only feels a component of that force (feels it in the direction you were original pushing I mean - imagine a train on rails). If you draw a vector diagram (that is GCSE!!! isn't it?) or use simple common sense then it's obvious that the force the object feels in the original direction you were pushing is the cosine of the angle you've turned through away from "square on".

Edited by RobM77 on Friday 23 July 14:27

[AdeTuono]

kazste said:

Not meant ad an insult bit Feck me you must be old to of done that in gcse. My gcse math was add this up and can you divide that (im 30) half way through hnC engineering and completely unprepared after what school taught me years ago with regards to the math I am having to do.

Edited by kazste on Friday 23 July 14:10

How'd you get on in English Language?

[onomatopoeia]

Lucas CAV said:

dpbird90 said:

Fantastic guys, many thanks. Yes, it is a first year University question, probably covered in A Level Physics but I didn't do physics, I was intending to do chemistry but when it came to making uni choices engineering and maths seemed much more appealing.

Your're going to have fun doing Engineering at university with no Physics A level...

Good luck!

I'm astonished that any university would take a Mech Eng student without decent A levels in maths and physics.

When I went through UCCA in 1986/7 I needed an A and a B in maths and physics (didn't matter which way round) to get into any engineering degree at a decent one

[dpbird90]

onomatopoeia said:

Lucas CAV said:

dpbird90 said:

Fantastic guys, many thanks. Yes, it is a first year University question, probably covered in A Level Physics but I didn't do physics, I was intending to do chemistry but when it came to making uni choices engineering and maths seemed much more appealing.

Your're going to have fun doing Engineering at university with no Physics A level...

Good luck!

I'm astonished that any university would take a Mech Eng student without decent A levels in maths and physics.

When I went through UCCA in 1986/7 I needed an A and a B in maths and physics (didn't matter which way round) to get into any engineering degree at a decent one

I'm not actually doing the full Mech Eng degree, I'm doing Mathematics and Engineering Mathematics, where most of it is maths, and the engineering bits that we do are all maths related (hence the structural mechanics), and hence they did not ask for physics. I did have the option to do extra courses as well, and last year I did the CAD drawing part of the engineering degree which was the best course all year

[RobM77]

onomatopoeia said:

Lucas CAV said:

dpbird90 said:

Fantastic guys, many thanks. Yes, it is a first year University question, probably covered in A Level Physics but I didn't do physics, I was intending to do chemistry but when it came to making uni choices engineering and maths seemed much more appealing.

Your're going to have fun doing Engineering at university with no Physics A level...

Good luck!

I'm astonished that any university would take a Mech Eng student without decent A levels in maths and physics.

When I went through UCCA in 1986/7 I needed an A and a B in maths and physics (didn't matter which way round) to get into any engineering degree at a decent one

Same here a decade later. However, if you could get in but flunked your maths most Unis offered foundation years or extra tuition after hours (depending on how badly you flunked your maths!). I was actually never very good at maths, but did ok at Uni because I preferred the teaching style. At school I just used to switch off after five minutes if the teacher didn't get to the point quickly enough!

[RobM77]

dpbird90 said:

onomatopoeia said:

Lucas CAV said:

dpbird90 said:

Fantastic guys, many thanks. Yes, it is a first year University question, probably covered in A Level Physics but I didn't do physics, I was intending to do chemistry but when it came to making uni choices engineering and maths seemed much more appealing.

Your're going to have fun doing Engineering at university with no Physics A level...

Good luck!

I'm astonished that any university would take a Mech Eng student without decent A levels in maths and physics.

When I went through UCCA in 1986/7 I needed an A and a B in maths and physics (didn't matter which way round) to get into any engineering degree at a decent one

I'm not actually doing the full Mech Eng degree, I'm doing Mathematics and Engineering Mathematics, where most of it is maths, and the engineering bits that we do are all maths related (hence the structural mechanics), and hence they did not ask for physics. I did have the option to do extra courses as well, and last year I did the CAD drawing part of the engineering degree which was the best course all year

Do they still have a choice of specialism at A Level Maths? When I did it you could choose between Maths with Mechanics (engineering Maths), Maths with Stats, or Maths with Pure Maths.

I'm just interested in how things have changed!

[ewenm]

RobM77 said:

I'm really not trying to sound big or clever here, and this is a genuine query, but is this really a University question?! I'm shocked! Maybe my memory is fuzzy (I left Uni 11 years ago), but isn't this one of the easiest questions from a GCSE Physics paper? Don't you learn basic trigonometry at the start of secondary school, and this is one of the ways you learn to use it in Physics?

I agree, GCSE level when I did them (1992 I think). SOHCAHTOA and applications thereof.