More HSC Qs (1 Viewer)

[Husayn]

OK so taking g to be 10 ms I get 4000, by dividing the 12000 N force by 3 (3 pulleys).

 

[SDuke]

I thought the calculation would be more complex then just dividing the counter weight by 3.

Dont u have to consider the efficiency, then work out the mechanical advantage.

Using the calculated mechanical advantage, and counterweight balance, i got tension to be 3.6GN.

And that's a huge number

....am i on the right track or completely off?

 

[Husayn]

The efficiency isn't given so you assume 100%.

It's:

MA = L/E

3 = 12000/E

E = 4000 N

 

[SDuke]

Lol, i got my MA as 300, forgot 100% is 1.0 not 100, i also thought 1.2 tons was 1200000kg....lol my bad

Thanks for clarifying the answer

 

[fakingtheday]

MA = L/E
3 = L/(1.2 x 1000 x 10)
L (tension) = 36Kn

EDIT: the counterweight is the effort, not the load.

 

[Husayn]

No problem, here's another 2004 question although it's theory - and seems like a common question:

 

[Husayn]

Yes fakingtheday that was a common error last year - as was said in the marking guidelines for 2004. The only reason I got it right was because I did around 50 of these questions today.

 

[Husayn]

For the aero one:

I'd pick the racing car and say materials used - strength-weight ratio. Also the aerodynamics of the car to reduce drag. For drag-racing, the fuel used for the turbo/exhaust or whatever its called and the compression of the air is related to the compression in that of an aeroplane.

Can anyone add anything?

 

[fakingtheday]

So i was right or you were?

And as for specific areas of design: racing car design. Dot points cause i'm lazy

* Apply benoulli's principle of airflow to car design such as air over the back aerofoil for maximum downward force and speed.

*Knowledge of composite materials for their strength to weight ratio to increase car speed.

Etc ect

 

[SDuke]

soz man, i'm crap with the whole aero course.

 

[Husayn]

It was 4000 fakingtheday.

------

Yes I think using those technical terms would yield more marks. So Bernoulli's principal and the aerofoil design.

Here's another one!

SDuke - Here's your chance to learn a few things, I certainly am.

 

[Husayn]

Well I'm pretty stumped for that one, I'd say that it is because of the damage caused to leading edges due to weathering?

 

[fakingtheday]

The leading edge of the propellor is more exposed to the direct force of the wind, and as we know cyclic loadings, especially wind leads to fatigue. The timber is there because it can be easily inspected and changed at regular intervals and is much cheaper than putting an expensive composite there.

 

[Husayn]

OK - so 1 mark for damage and 1 for cost seems reasonable.

 

[SDuke]

wat's cyclic loading?

 

[Husayn]

That's obviously related to hydraulics, I'll leave to fakingtheday for the technical answer - if he's willing

 

[fakingtheday]

Pleasure sir: cyclic loading is bacially from aero. It's repeated stresses, and in the case of fatigue, it's stresses much below the acknowledged maximum stress. That's why in the old days planes would sometimes just fall out of the sky.

As for the efficiency. ABS brakes senses brake locking resdistribuets braking pressures and stresses on pads therefore increasing efficiencies. (dodgy but close enough)

 

[SDuke]

Thanks for the cyclic loading explanation

 

[Husayn]

Gotchya, ABS. Must remember that.

I would say asphault for its resilience and relatively un-abrasive surface, and the re-inforce concrete for its appropriate tensile/compressive strengths which are necessary for the cantilevar design.

Good enough?

 

[fakingtheday]

full marks sir, we had that one in our half yearly. That's a perfect answer.

EDIT: you could also say that asphalt wouldn't mix with the soil fill