Structures and Materials Question

[Lols123]

Question 10
Shouldnt part of the beam be under tension at the bottom, since its a cantilever?

[dopplereffect]

How can on one side half be in tension and the other half be in compression? It can't. Imagine if the block at B wasn't there.

[Lols123]

what...thats how cantilevers normally work...

[thushan]

Not necessarily true. Repeat the question, but stick a piece of rope in rather than a plank. The rope would sag between A and B.

edit: directed at doppler.

[dopplereffect]

I imagined the question like a real life diving board, when you apply a force on the end the whole top of the material is in tension.

[acinod]

Chemology 2011 also had a diving board question.
It asked which is true of the forces on the diving board:
A. The board is under compression
B. The board is under tension
C. The top of the board is under tension and the bottom is under compression
D. The bottom of the board is under tension and the top is under compression

The answer was C as the board will bend under Bella's weight. Thus, steel rods should be placed entirely at the top which is under tension.

[dopplereffect]

That's where I remember doing this question before.

[thanh123]

that was a simple question.
because the bottom will compress the top must be in tension THE WHOLE WAY

[Thelimz]

if i lost 3 marks, is that 50 material?

[thushan]

that was a simple question.
because the bottom will compress the top must be in tension THE WHOLE WAY

Just had a chat to an assessor, he went with D. Most likely though they'd accept both.

[examsman]

How the fuck do you get to have a chat with an assessor?

sorry, D as in the whole of the top was in tension?

[thushan]

He's one of our teachers at school....

Oh and whoops i just realised, I shouldn't have said "just," i had the chat straight after the exam.

No, D as in the ___------------ answer.

[examsman]

Well, thushan, I can't agree with that, about the pivot point, it is clear that directly to the left and right will be in tension, so yeh...

[thushan]

Fair enough, we'll see.

[Asx4Life]

It's definitely A, the centre of mass of diving board was past the pole thing so the wall thing had to exert a downwards force to balance the structure!!