Engineering Marathon (4 Viewers)

[00iCon]

Q: describe the logic gates (i think there's 6).

 

[Kaos1]

logic gates? ive never heard of any gates in engineering... please elaborate on that question

 

[qwertyuiop1234]

The basic three logic gates are AND, OR and NOT. The and gate needs both inputs to be 1 (true) in order toget and output of 1. In all other cases the output is 0. The OR gate only needs only variable to be 1 to get an output of 1. The NOT gate is like an addition to the other two. If the variable is 0 (false) then it will go through as 1. Basically switches it.

Q. Explain Bernoulli's principle and its application to planes.

 

[bossleymaths]

Q: describe the logic gates (i think there's 6).

theres:

AND, NAND, OR, NOR, XOR, XNOR

those are the 6 but the most important to know are the first four.

this is this AND that.

this is NOT this AND this

this is this OR that

this is NOT this OR that.

haha i just made the sentences up, but u get the idea

 

[bossleymaths]

bernoullis principle is essentially about how the bigger the velocity the the lower the pressure and vice versa.

applications: this is seen in aerofoils on planes, on flaps, wings, aeilrons etc etc and it usually provides a greater velocity (lower pressure) on top of the wing due to wind.

 

[bossleymaths]

QUESTION

outline the heat treatment processes for duralumin (an aluminium alloy used in aircraft mostly) and also the manufacturing processes.

 

[Kaos1]

bernoulli's principle works around the idea that as air accelerates, it looses pressure, and visa versa.

the use of a venturi tube clearly shows this: the air to begin with has a constant velocity, and a constant pressure, as the air is forced into a smaller opening, it speeds up and thus looses pressure, as the air exits the smaller opening, it slows down to its original velocity, and its original pressure.

this applies to the aerofoil aroung an aircrafts wing. the top of the wing is shaped to force the air up and over its surface (thus speeding it up and decreasing its pressure), whilst the bottom of the wing is relatively flat (thus maintaining the pressure it had originally).

the potentiial difference between the air above and the air below the wing literally sucks the wing into the air (air tends to move from high to low pressure; the constant pressure below the wing tries to get to the lower pressure above the wing)

there are variations to this principle which can be achieved by varying the shape of the aerofoil.

BUT bernoulli's principle is only half of the required infomation needed to achieve flight in an airceaft. the other half is the 'angle of attack' of the aircraft

define 'angle of attack'

after you have answered that, answere this next question that i am stumped on (2007 hsc paper, question 18, ii)

in another situation, the load on the winch cable is 1100N. the cross sectional area of the cable is 37mm squared and the youngs modulas of the material is 210GPa.

calculate the extension that would occur in a 10 meter length of cabel material.

show all working out

 

[qwertyuiop1234]

in another situation, the load on the winch cable is 1100N. the cross sectional area of the cable is 37mm squared and the youngs modulas of the material is 210GPa.

calculate the extension that would occur in a 10 meter length of cabel material.

show all working out


A.
E=210*10^9
A = 3.7*10^-5
L = 1100
l = 10

stress = L/A
= 1100 / 3.7x10^-5
=29729729.73 Pa
E = stress / strain
Therefore strain = 29729729.73 / 210 x10^9
=1.4157 x 10^-4
strain = extension/original length
1.4157x10^-4 = e/10
therefore e = .0014m
=1.42mm

 

[qwertyuiop1234]

Angle of attack is the angle that a wing or blade (helicopter) is at. When angles above the horizontal are used lift is produced but when angles below the hoizontal are used the craft will go down. A helicopter blade must change its angle of attack every half cycle in order to continue going up and so it won't roll.
Q. Describe Archimedes principle and its application.

 

[Kaos1]

you see... i got .0014 aswell... but i went a totally different way...

please correct me where if i went wrong

E = FxL/Axe
(youngs modulas = (force x length) over (area x elongation)
therefore
2.1x10^8 = (1100 x 10) / (37^2 x e)
e = 1100 / (2.1x10^8 x 37^2)
= .0014

is that correct?

 

[qwertyuiop1234]

QUESTION

outline the heat treatment processes for duralumin (an aluminium alloy used in aircraft mostly) and also the manufacturing processes.

duralumin is an alloy of aluminium and copper and is usually heat treated using precipitation hardening in which it is heated to approx 530 degrees celcius to produce a single phase alloy and then it is quenched to room temp. The second trapped phase slowly precipitates on to the stress planes and strengthens the alloy. Sorry too much of an idea about the manufacturing processes.

 

[qwertyuiop1234]

you see... i got .0014 aswell... but i went a totally different way...

please correct me where if i went wrong

E = FxL/Axe
(youngs modulas = (force x length) over (area x elongation)
therefore
2.1x10^8 = (1100 x 10) / (37^2 x e)
e = 1100 / (2.1x10^8 x 37^2)
= .0014

is that correct?

Yeah i'm pretty sure thats right and essentially it is the same way of doing it its just you use the nice simple formula and i did the long way around it, lol

 

[Kaos1]

aaaah ok then, kewlies, thank you

sorry, i know nothing about archimedes. can someone else answere it?

 

[yz125]

aaaah ok then, kewlies, thank you

sorry, i know nothing about archimedes. can someone else answere it?

Okay, i'll give it a go. Basically when you place an object in a liquid (such as water) the liquid provides an upward force that reduces the weight object.

When a body is completely or fully immersed in a fluid it experiences an upthrust or apparent loss in weight which is equal to the weight of the fluid displaced.

upthrust on body = weight of fluid displaced

Question: Describe the process of sand casting

 

[qwertyuiop1234]

Sand Casting. Sand is packed around a finished model and binded so it stays in the same shape. Molten metal is the poured in and allowed to set. The two halves of the sand cavity are taken away leaving the metal. The sand can be reused.
Q. Explain the most common type of moulding for polymers

 

[Kaos1]

i forget the exact name... rotational moulding, shell moulding, im not sure what it is...

but it where a molten polymer is poured into a hollow mould of an object. the mould rotates around 3 axis so the polymer has an eaven coating around the outside. its left to dry. the mould comes apart in the centre, and the polymer object is left behind

a stainless steel cable is made of multiple strands and wires. detail why this configuratyion is better (stronger, durable, felxible, watever) then a single piece of metal of the same radius as the thickness of the entire cable

 

[arman]

I managed to get AB as 16.28822036 kN tension.

A brief description of how I did it.

I got the angle under the bridge 12.52880771 (the line from RB to B and the angle between that to horizontal). Using this angle, I then got the vertical distance from the horizontal to B by using trig with the 3m that is given. This distance was 2/3 m.

Now having this distance, I could get the hypotenuse which is RB to B and also the distance of the vertical bar from B. RB to B is square root of (85/9). The distance of the vertical bar from B is 2 and 1/3 m. (3m subtract 2/3 m).

Now cutting it and looking at the RHS, I summed it at B (canceling AB and the hypotenuse I was talking about), and got the top bar's force. I got this as 87 1/7 kN in tension. (This will be useful later on)

Now I look at the LHS. Using the hypotenuse distance square root of (87/9) and also the 3m given I get the area of the triangle RB - A - B. I do this by using 1/2*a*b*sinC. C is worked out by 90 degrees minus the angle under the bridge. (90 - 12.52880771 = 77.47119229). (I get area as 4.5m^2)

Now this area has to equal the other area equation, 1/2*base*height. The height is always perpendicular, so this is what I want, as it is the perpendicular distance from AB to RB. So I need to base, I calculate the base by using a^2 = b^2 + c^2 - 2bc*cos angle. The a is the base, and the rest are form the triangle. I calculate the base as 3.80058475m. Thus height is 2.368056652m. (This is the perpendicular distance between the line AB and the point RB).

Now I sum it at RB, since I sum at RB, the horizontal component of RA is canceled and the force on RB-B is also canceled. This leaves the vertical component of RA (100 kn), AB and the top bar (87 and 1/7 kn in tension).

Thus, 0 = (-100) * 3 + (87 1/7) * 3 + AB * 2.368056652.

AB = 16.28822036kN tension.

I have no idea if this is right. This process is so convoluted that there is a high chance of error throughout the process. What do you guys think?

There must be a better and simpler way than this.

I'll name RA and RB C and D respectively.
There is a reaction Cx, Cy and Dy.

Fx = Cx+10 = 0
Cx = -10 kN

Fy = Dy+Cy - 30 = 0
Dy+Cy = 30

Mc = 3Dy - 30*12 - 3*10 = 0 -> Dy = 130 kN
Thus, Cy = -100 kN

Using method of sections (cbf having the diagram here) -

The angle RB is atan(3/14) = 12.1*

The height of the triangle RB-B is 3tan(12.1) = 9/14
Thus the triangle AB has a height 3-(9/14) = 33/14

angle at AB is arctan((33/14)/3)) =38.16*

Now analysing the section -

Fy = -ABsin(38.16)+RBBsin(12.1) =-30
Taking the moment at A -
Ma = -(-100)*3+(-10)*3+RBBcos(12.1)*3 = 0

so RBB = -92.045 kN

Solving above
AB = (RBBsin(12.1)+30)/(sin38.16) = 17.327 kN so AB is in tension

Ok, those answers are close. I asked my engineering teacher today, he said consider RHS of truss, and do in two steps using method of sections.
He said don't bother about finding length of vertical member at B as it is too time consuming and so I assumed that length as 1.7m and got an answer of 14. sumthin Kn

Sand Casting. Sand is packed around a finished model and binded so it stays in the same shape. Molten metal is the poured in and allowed to set. The two halves of the sand cavity are taken away leaving the metal. The sand can be reused.
Q. Explain the most common type of moulding for polymers

Injection moulding as plastics have high fluidity when melted ... any1 else to elaborate?

 

[arman]

Can someone please...

Briefly outline the different molding techniques for polymers

 

[qwertyuiop1234]

a stainless steel cable is made of multiple strands and wires. detail why this configuratyion is better (stronger, durable, felxible, watever) then a single piece of metal of the same radius as the thickness of the entire cable

The smaller strands have less likelyhood to be flawed (surface cracks etc) and therefore will stand up to more bending, stretching. It is also better because if one strand breaks than the rest of the strands can take up the slack and the cable will still operate whereas in the single strand if it breaks its all over.

 

[tommykins]

Ok, those answers are close. I asked my engineering teacher today, he said consider RHS of truss, and do in two steps using method of sections.
He said don't bother about finding length of vertical member at B as it is too time consuming and so I assumed that length as 1.7m and got an answer of 14. sumthin K

as if, i triple checked my answer and i'm 99.9999% sure it is right.

as if you can't find the length of the vertical member B, what? can't your teacher do simple trigonometry or similar triangles?

the length is not 1.7 .