For You Physicists, Mathematicians And Engineers Out There.

[DTCwordfan]

I have sent this one to Facto-fiction for his thoughts but then it may be fun for some of you, particularly where you need to stretch the old physics brain.

It comes of problem solving with a 14 year old, that described his Dad as being and Mum as being crap at the subject and who called me.....not sure that I am much better and just wanted to test what I think is the solution - that's with Factor but I thought I'd put it here and you your solution and logic.

The problem:

Imagine or draw a distorted "U" shaped tank, one that has a wider top of the "U" on the right than the left, area 10cm2 on the left and 200cm2 on the right.

One the left hand side there is "plunger" with a pivot on the bar and the distance of the bar from left to the pivot (A to B) is 1 meter and (B to C) 0.1m)

Upward force on the lever at A (very left hand side is 50N).

The questions being

1. the pressure on the left pipe? (I assume it is water in it)

2. The load on the right.

[gen2]

1. 50N/sq cm
2. 10,000N
by my calculation

[DTCwordfan]

That's what I have gen - wasn't sure whether you were supposed to turn the cm2 into metres2.

[gen2]

You didn't say what units you wanted your answer in.
The lever lengths were quoted in metres, but the area in square cm.
I wondered whether they wanted the pressure in Pascals
1 Pa = 1N/sq m
50N/sq cm = (50*10,000)N/sq m
so 50N/sq cm = 500,000Pa or 0.5 MPa

[DTCwordfan]

Thanks gen - no, don't think he needs that yet (the Pascal) - that came after my time. The good thing was that he understood the concept as I chatted away with his parents for 20 mins and then asked him to explain how we had put the calculation together and he was ok with that....so if he gets asked whether he was helped, he can say yes but I understand the logic now. He has been upgraded in his school but is having to do "catch up".

Glad to know that my grey cells are not totally brain-dead either!

[gen2]

. . . unless of course we are both equally brain dead :-(
Whatever happened to the ergs, dynes and poundals of our schooldays?

What did Factor (30) Fiction come up with?

[DTCwordfan]

Waiting to see that, gen

[factor-fiction]

Hi DTC- well I must confess I couldn't understand the problem- I couldn't visualise the position of the bar and the distances AB and BC. But given that you and gen arrived at the same answer independently I'm sure you're right.
I must say though that for a 14 year old this is a pretty stretching problem. Most 14 year olds would come unstuck when asked how many centimetres in a metre- last time I asked that I got a row of blank faces and then someone said "how am I supposed to know that?", so I passed her a metre ruler and she studied it and said "about 97?"

[gen2]

This is how I pictured it:

http://gentoo2.multiply.com/photos/album/45/For-AB#1

[DTCwordfan]

You are absolutely on the money with that graphic, gen, well done! I had this paper version but I am away from one of my home bases and don't have a copier here!

Many thanks....

yes, factor, I thought it fairly stretching - he has been promoted in class midyear and is struggling to catch up and I must admit that I think I would have been baulking at this one at his age, even though I did my O levels at 14, partly given my birthday, "A"s at 16 as a consequence and then a gap year before it was fashionable to call it that.

[gness]

So...its Friday night.....end of a long week...bottle or two opened...feet up...... relax....... and DT comes up with this!

[DTCwordfan]

got to stretch those brain cells a bit, gness, so as to pack in a little more red vino, guinness, and a lake of other ethanol-based poisons

[DTCwordfan]

sorry for dropping the r, factor, though "facto-fiction" does read rather well, IMHO