Brain cells needed - 1955 test

Agreed, but until the joints do pull out it is going to do better than the unbraced ones. They didn't ask if they were sensible designs!

Your point is valid, and inablity to search text is a major nuisance even if one can see the pdf. But in this case the text consists of short, simple questions about hand-drawn sketches of mechanisms, and the text would really not help at all.

It was a while ago. I'll ask him but I suspect seeing an experiment demonstrated once is the same as having personally tried it and got it wrong many times. For instance the tent peg question.

A bit of experience with Meccano would help a great deal, to understand the importance of diagonal cross-bracing of a rectangular shape (eg the gate in one of the questions) or to understand meshing of a train of gears. Sadly modern children don't seem to "play" with Meccano any more. I use the word "play" in its widest sense to mean build things and work out by trial and error what is good and what is bad and how to improve what is bad.

The questions that I need to think about are the tension/compression forces in various struts on lattice structures, and which will be largest/smallest. I did a bit of mech eng on my elec eng course, but I don't know as much or know the rigorous analysis techniques that a civil eng would know.

The joints were clearly pins able to take compression or tension as well.

The one with the weight hanging off rope at the top of the well? There's enough information there.

Lego Technic offers the same opportunity.

Here are my answers with reasoning:

1. C
2. G goes deepest into ground while being angled towards the pulling force (at 45 degrees)
3. M area is s^2 rather than pi (s/2)^2 (where s is the length of the side or diameter)
4. Q closest to the pivot: need greatest ratio of length of handle side to length of twig side (lever - maginfication of force inversely proportional to distance from pivot)
5. All equal (not entirely confident on this one)
6. A smallest radius
7. H cross-brace, even if it *is* in tension rather than compression!
8. O greatest number of pulleys
9. move to and fro
10. V if the objective is to prevent the hanging rail bending/breaking
11. B smallest surface area of liquid and smallest area of cup
12. F and G (H turns in opposite direction)
13. N at pivot, with greatest distance and therefore greatest turning moment from children on either end)
14. Fall radius of "fall" side of rope is greater than radius of "rise" side
15. X 45 degrees
16. D longest length of strut from its pivot
17. H load is carried closest to the pivot/wheel, with longest distance from load to handle
18. L narrowest arch relative to height
19. S goodness knows - hard to estimate how the curved line continues
20. V longest anchor line so greatest component of force sideways compared with vertically
21. C if same amount of energy (mgh1-mgh2) = (mgh2-mgh3) is lost on each bounce
22. J smallest surface area so smallest air resistance
23. N roughly in same direction as line through centres of white and black balls
24. fall balls fly outwards, causing collar to rise and hence pointer to fall - a governor
25. W guessing - not sure
26. rise and then fall: pipe that fills X is bigger than one that drains it so inflow is greater than outflow
27. H furthest away from either end (eg F) where it will stop and reverse
28. O greatest turning moment furthest from pivot
29. R others will roll freely only until off-centre bar is at bottom and will experience retarding force after that
30. W greatest mass concentrated furthest from centre
31. D because he's having to bank over furthest to compensate for (mv^2)/r centripetal force
32. move in circle (both small cogs are same radius and will turn in same direction, so no jam)
33. S closest to centre so he's exerting least turning moment to overcome whatever the capstan is turning
34. X resultant force is midway between directions of pushing forces
35. smallest radius of curvature so greatest (mv^2)/r centripetal force (assuming all cars doing same linear speed)
36. H
37. one ball hits the group of four so one ball leaves group (as for Newton's Cradle)
38. all equal
39. opposite, unevenly (won't jam because ends of rod are 180 deg out of phase so no vertical component to motion)

I'm open to argument/correction on some of them!

You do not need to you can see where the mark is rubbed out.

I had in mind the nautical capstan with 4 men and "Which man would have to work hardest to turn the capstan alone?" ISTM "hardest" is ambiguous between (a) the force exerted (highest for shortest lever), (b) the energy required per unit time (ditto if they walk at the same speed - linear not angular - when walking alone), and (c) the energy required per revolution (same for all).

yep. That was another one I noticed

Then there were the eccentric weights rolling down an inclined plane. Well it depends HOW eccentric the weights were and how steep the plane was.

No Bill, It does not

No, Bill. the joints are tenoned and pinned . They cant pull out.

This is utterly basic.

No, I think not the capstan.

The point of a capstan is to allow leverage and the further from the hub you are the less force is needed for a given action

A perfectly valid answer IMHO!

No it's fine to do it the other way if you don't mind the gate pulling apart when a child swings on it.

Granted that is the traditional way,

Because it works much better. There's a reason for most traditions.

How would you do that? Very difficult to get the same strength as doing it the correct way would.

If it relies more heavily on the fixings it's not as good a design. If extra stress can be avoided it should be.

It's the correct answer but it shows that the author has no idea about basic joinery techniques.

Bill

No, it just shows that the author was an ignoramus. I bet he didn't do woodwork at school.

Bill

Another question with no unconditionally correct answer. It would depend partly on the ground conditions, as anyone who has done a lot of tenting would know full well.

bill

Ah, right, fair enough.