# Chapter 2

• 13 September 1996

The last two years at school felt really long. But now it's finally over. After so many years of studying, I've made up my mind: I've had enough of books! It's time for me to earn some money and become financially independent. Mum and dad aren't happy with my decision at all! They insist that I sign up for university, but I'm tired of being a financial burden. I need to stand on my own two feet from now on. They asked me to think it over, but I've decided to follow my intuition and already applied for a job as a mechanic. And my first interview went really well! They seem to like me and they've now sent me a mechanical comprehension test to see if I'm suited for the job. I could ask dad for help, but I won't. It was my choice to pursue this path, so I'll handle the difficulties it brings on my own as well.

Mechanical comprehension test:

Q1: Which wire is carrying the most weight?

1. A
2. B
3. No difference
4. Depends on the time of day

Q2: Which object will not float on water?

1. Empty plastic bottle
2. Wooden pencil
3. Banana
4. Scissors

Q3: Which way will the boat go through the water?

1. A
2. B
3. It will continue moving unchanged
4. It will slow down but without changing direction

Q4: At which position will the moving pendulum travel the fastest?

1. A
2. B
3. C
4. No difference

Q5: Where is the temperature change highest throughout the day?

1. A
2. B
3. Where both meet
4. No difference

Q6: If cog A turns clockwise by 20 rotations, how will cog B turn?

1. 20 rotations anticlockwise
2. 20 rotations clockwise
3. 10 rotations anticlockwise
4. 10 rotations clockwise

Q7: To balance the bar, how much weight should be positioned on the left side?

1. 25 kg
2. 10 kg
3. 5 kg
4. 2.5 kg

Q8: If block B is moved to the right by 20 cm, by how many centimetres will block A move upwards?

1. 5 cm
2. 10 cm
3. 20÷3 cm
4. 20 cm

Q9: A block slides down an inclined plane with an acceleration of A. If the mass of the block is doubled, how will this affect its acceleration?

1. Acceleration will still be A
2. 2 x A
3. 0.5 x A

Q10: If the right plunger is moved down by 5 cm, how much will the left plunger move up?

1. Exactly 5 cm
2. Less than 5 cm
3. More than 5 cm
4. It won't move

• 1 point for each correct answer

• Q1: B

Q2: scissors

Q3: A

Q4: B

Q5: A

Q6: 10 rotations anti-clockwise

Q7: 2.5kg

Q8: 20cm (assuming pulleys are fixed)

Q9: still A (assuming there is no friction)

Q10: Less than 5 cm

• Q1 - 2

Q2 - 4

Q3 - 1

Q4 - 2

Q5 - 1

Q6 - 3

Q7 - 4

Q8 - 4

Q9 - 1

Q10 - 2

• 1. It seems with no difference (answer 3), but reverse picture is a proof, less spin and so less weight is on wire A (small end of "Bat"). So most weight is on B (Answer 2)

wbb.rail-nation.com/wcf/index.php?attachment/23426/

2. Q2: Which object will not float on water?

1. Empty plastic bottle - "empty" = full of air (then swim)? full of vacuum? If it is hard enough then will float on water (->swim), but if it is weak bottle (Try to suck the air out of the "empty" bottle, and the bottle splasts, and then sink), this is the same as fill it with water, in which the bottle has to swim and the bottle sink
2. Wooden pencil - swim
3. Banana - I had to go to the store and buy bananas, and make an attempt... Bananas swim..
4. Scissors - usually metalic with a piece of plastic - sinking

4. From A to B or from C to B is gravity adding power. from B to C or from B to A is removing, so in B is power biggest, and also speed. in A or C is speed smaller, and/or can be 0. on B is pendulum fastest, answer 2

5. on sand (answer 1), water accumulate heat (or cold) and hold it for a long time, sand accumulate heat (or cold) and releases it soon

6. 10 rotations anticlockwise (answer 3), each conversion changes direction (3 changes: small>(1)bigger>(2)biggest>(3)bigger)… 20 turns of sprocket (x 5 cog(tooths) is 100 tooths), last sprocket have 10 tooths, so 100tooths/10tooths of last sprocket is 10 turns of last spocket...

7. lever - twice distance is halved power (weight), so 2,5 kg (answer 4)

8. pulley… this is not hoist, so 20 cm - answer 4. hoist is below (then it will be 20/3 cm)

wbb.rail-nation.com/wcf/index.php?attachment/23432/

9. acceleration is independent to mass or density of block, no change, still A, (answer 1)

10. volume must be the same, 5 cm of thicker plunger equals less than 5 cm wider plunger (answer 2)

• Oh my... I actually went to the kitchen and checked that a banana floated! WHAT ARE YOU DOING TO ME!!!!!!

I didn't do physics or mechanics ever, so this answer is the result of personal investigation (see above) and an exploration of google.

Q1) 2 (couldn't track this answer down - going with common sense)

Q2) 4 (my banana floated - who'd have thought it!)

Q3) 1 (gotta love boats)

Q4) 2 (youtube vid on pendulum - learned about potential and kinetic energy - wow!)

Q5) 1 (knew my beach holidays would come in useful)

Q6) 3 (I now have finger marks on my computer screen... thanks :/)

Q7) 4 (you tube and pivots and balances... cool)

Q8) 4 (pullies! So by the look of things you have 3 single fixed pullies - which won't do anything sensible. I'm assuming that you are not using elastic as your connecting material, otherwise it won't move at all!!!)

Q9) 1 (youtube again - says acceleration isn't affected by mass - go blame them if this is wrong!)

Q10) 1(Fluid dynamics??? What even is this stuff - I don't follow this at all, but it looks like the pressure of water stays the same… huh? Maybe?

I am now late for the dentist.....

• Q1: 2 (B)

Q2: 4 (scissors)

Q3: 1 (A)

Q4: 2 (B)

Q5: 1 (A)

Q6: 3 (10 rotations anticlockwise)

Q7: 4 (2,5 kg)

Q8: 4 (20 cm)

Q9: 1 (Acceleration will still be A)

Q10: 2 (Less than 5 cm)

• Q1. 2. B, if the density of the material is uniform.

Q2. 4. scissors, especially metal ones.

Q3. 1. A

Q4. 2. B (I'm presently teaching potential energy in my Physics class - I'd best not miss any! :O )

Q5. 1. A

Q6. 3. The rotations anticlockwise

Q7. 4. 2.5kg

Q8. 4. 20cm ... hoping all the pulleys are fixed in space

Q9. 1. Acceleration will still be A

Q10. 2. Less than five cm

• Q1 B

Q2 Scissors

Q3 A

Q4 B

Q5 A

Q6 10 rotations anticlockwise

Q7 2.5 kg

Q8 20 cm

Q9 Acceleration will still be A

Q10 Less than 5 cm

• q1 2

q2 4

q3 1

q4 2

q5 1

q6 2

q7 4

q8 4

q9 1

q10 2

• 1 = 2

2 = 4

3 = 1

4 = 2

5 = 1

6 = 3

7 = 4

8 = 4

9 = 1

10 = 2

• Q1. 2

Q2. 4

Q3. 1

Q4. 2

Q5. 1

Q6. 3

Q7. 4

Q8. 4

Q9. 1

Q10. 2