# Semi-trailer (1 Viewer)

#### Husayn

##### Banned
What did people put for this question? Use of the canopy etc...

#### indeecent

##### New Member
well it has an aero effect so the actual trailer doesnt have a direct force of air on it

and it was out of fibre cuz its easy to produce, cheap, easy to repair, and the resins are mostly impervious to water

what did people get for the amount of slats the truck can carry? i got 9 :S

#### chaotichampster

##### New Member
Canopy is used for aerodynamics. Fibres are Lightweight and easy to mould into shape.

They should be smooth for air resistance and aesthetically pleasing (woot cheap answer)

For the slabs i got 4, which most of our guys got.

#### indeecent

##### New Member
yeah, i was afraid of that, but when i worked it out, the usable force is 78000N, which works out with 9 slabs, when u use sin instead of cos it works out as 4, so i duno, SOHCAHTOA, to me i thought since its an adjacent angle, its cos...

#### MalaukuS

##### New Member
chaotichampster said:
Canopy is used for aerodynamics. Fibres are Lightweight and easy to mould into shape.

They should be smooth for air resistance and aesthetically pleasing (woot cheap answer)

For the slabs i got 4, which most of our guys got.

Yeah that was basically the gist of my answers.

#### SDuke

##### Member
Damn, i got the number of slab as 109, lol. i knew i was wrong but not by a factor of 10.

#### indeecent

##### New Member
anyone proved my 9 wrong? check it please, SOHCAHTOA, cos = adjacent over hypotanuse, which is what we are finding there, so the 80000N should be times by cos 11.3, and then u end up with 78000, - the 10, then divide by 7.5, and u get 9... if im wrong, someone please prove it

#### morty87

##### New Member
yeh i got 4 slabs aswell and its really annoying how everyone has a different answer to this question, everyone in my class had something different too. can we please get a confirmation on this question, most prefrebly from fakingtheday, thnx alot, 4 slabs all the way

#### Husayn

##### Banned
The weight component of the thing parallel to the slope is sine. Perpendicular the weight component is cos.

#### mattplaysguitar

##### New Member
Yeah!! Go the 4 slabs!! i worked that question out with PE. i drew up the slope then worked out the hight the truck had to climb, then u could work out the potential energy at the top, so this was the amount of energy u needed to put in. then u make up a simple formula with N as the no. slabs, and it came to about 4.something so i said 4 slabs. i know at least one other person in my class got that. overall id say its either 4 or 9, but i think i have seen more 4s, so im going for the 4s

#### wonko

##### New Member
i still have so much trouble with the up hill energy etc ones,
i mean no one in the state got my answer negative 75 slabs
oh well i never have to worry about it again
right now i'm frantic about english tomorrow-i don't know any of my texts well enough to write essays-they just weren't interesting

#### aerohydro

##### New Member
hey what do u guys all use for gravity? i used 9.8m.s^2 and i got like 3.9998 slabs so i put 3. maybe i just stuffed up the rounding or something, but its all there so its ok i guess.

#### Necros87

##### meh
if they dont specify a value for g, you can use whatever you want, within reason and your ment to tell them what you use, eg. on side of paper g=10

#### fakingtheday

##### Member
Hey guys, i had 4 slabs. This really could go either way. I used exactly the method Matt did. Made sense at the time, standing by it.

However, the question is wrong in that driving force cannot remain constant if the velocity is too. But 4 seems more correct because 67.5 Tonnes is A LOT of weight for a truck to carry, and this is a practical subject. I wish the people who set this would show some common sense.

#### jbo69

##### New Member
hey all, i got 4.1 but rounding it to 4, the formula's i used were p=w/t, which i found the max work it can do, then i used f=ws, and found the max force, then i found the force the truck would give out with no slabs, then subtracted the force from the truck form the total force, then with the remaining total force u convert to kg, then work out how many times 7.5 tonne goes into the mass. and i got 4.1 in my calculator, so i got the four!!! sounds confusing!!

##### Member
Lol...that section on top of the trailer, lets be real...its used for the driver to sleep in

#### mattplaysguitar

##### New Member
i just remembered something about the multiple choice question using bending moments and second moment of area. i got an answer which was of the same numerical value to part d, but it was like 6 decimal points out, is second moment of area meant to be to the power of negative 6? i cant remember entirely, but yeah, anyone alse notice anything about that question at all?

#### stv_87

##### New Member
i got a similar thing with like 10 nunmbers on my calculator but had the 1547 or something but looking back for some chaotic reason i guessed a different one. stupid

##### New Member
Lol...that section on top of the trailer, lets be real...its used for the driver to sleep in
Please tell me you wrote that!!!