I like puzzles, but the math puzzles in the other thread are too hard for me. So why not start a thread for puzzles in an even more interesting field of study : physics!

Let's start with this one:

You are in the basement of a building. There are three switches, which are all in the off position. You know that exactly one of the switches is connected to a light bulb in a room in the first floor. However, to check if the light went on, you will need to take the elevator to the first floor and check the room. Now you are allowed to use the elevator only once. How do you figure out which one of the three switches controls the light?

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Stay out of my territory! (W. White, aka Heisenberg)

A. flip switch 1 to "on"
B. wait several years
C. flip switch 1 to "off", switch 2 to "on"
D. Ride elevator.
* Burned out bulb = switch 1 controls the light
* Bulb on = switch 2 controls the light
* Bulb off = switch 3 controls the light

Is that it? I'm guessing there is a more elegant answer, but I think my solution will work.

You're close, but a bit destructive. You can simply wait a few minutes until the lightbulb gets warm and check its temperature instead of waiting until it dies.

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Sanity is for the weak.

Switch 1 - on for two minutes, then...
Switch 1 - off.
Switch 2 - on
Switch 3 off.

Jump in the elevator (quick!) and go up to the room.

If the bulb is off AND warm - switch 1 controls it.
If the bulb is off AND cold - switch 3 controls it.
If the bulb is on AND not warm - switch 2 controls it.

Is that right?

EDIT: Bummer, beaten to it.

Ha! I was closer than I thought.

OK, here's another physics puzzle (well, maybe not physics, but some branch of science is involved):

There is a lake. It's like a giant bathtub - no water in, no water out. A guy is in a boat in the lake, with a rock in the boat. The guy takes the rock out of the boat and drops it into the lake; it sinks to the bottom. After the rock is dropped in, is the water level of the lake higher, lower, or the same?

Suppose for an eay argument that the floor of the pool is horizontal and the sides are vertical. With the rock on the floor the pressure exerted by the area under the stone is bigger than the upward pressure exerted by other parts of the floor. The total upward force exerted by the floor of the pools remains the same. ( If you dont believe try lying under it ). Thus the upward pressure exerted by other parts of the floor has decreased after the rock landed. So the hydrotic pressure and hence the depth has and hence the water level has decreased. Another question is when the water level decreased. When the rock is held under water, when it was released or when it landed.

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I think I am so I think I am.

My answer is...

What if they are fluorescent bulbs?

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Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

Another one: you forget the refrigarator open. (Why) Will the room temperature increase or decrease?

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If you say no, Elwood and I will come here for breakfast, lunch, and dinner every day of the week.

Question for entropi. How much of you is on a [font=]green[/font] photon.

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I think I am so I think I am.

Photon entropy is independent of color

But in fact my nickname refers to entropy in the sense of information theory which is the most basic and my favourite concept for understanding the nature of information, by Shannon.

Sverre's answer to my question seems to be correct.

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If you say no, Elwood and I will come here for breakfast, lunch, and dinner every day of the week.

Is it? Then it might be k, the Bolzmann constant, 1.380 6504(24) × 10−23 J/K.

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I think I am so I think I am.

cyclops, I liked your reasoning with the pressure, nice.

Well, it seems my first puzzle was not difficult enough for a smart croud like the one here on L19. Watch out: this one is REALLY cool, but also hard to figure out:

You have a ramp and you have two identical cans of soda. If you let both cans roll down the ramp, they will arive at the bottom of the ramp at the same time. Now if you shake one of the cans directly before the experiment, one of them will be faster than the other. Which one is it and why?
And if you do not believe that: try it out!

_________________
Stay out of my territory! (W. White, aka Heisenberg)

Well, I'm not a physics major, but I just attempted it and

I really don't have a good idea why.

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We don't know who we are; we don't know where we are.
Each of us woke up one moment and here we were in the darkness.
We're nameless things with no memory; no knowledge of what went before,
No understanding of what is now, no knowledge of what will be.

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Tactics yes, Tact no...

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If you say no, Elwood and I will come here for breakfast, lunch, and dinner every day of the week.

The title "Physics puzzles" reminded me of this one:



from xkcd

O.k.,
here comes my attempt for a nice contribution to this thread:


Late in the evening of a warm summer night, into the setting sun,
a very heavy freight train is pulled by a strong and heavy locomotive
onto its way to destination.

A tiny mosquito - may be it was an ephemerid ('one-day-fly' in German) - happened to hoover above the rails - when,
its honeycomb eyes blinded by the evening sun, it turns around and
WANG - its short life found an end.

There was a moment that the train (and perhaps insect?) stood still (had speed zero).
True or not?
_______________________________________________________________________________________________________________________
You know the 'Impulserhaltungssatz' (German for momentum conservation law (theorem) in physics)

momentum (SI unit kg·m/s, or, equivalently, N·s) is the product of the mass and velocity of an object (p = mv).

p = mv = constant,
resp. p1 x m1 = p2 x m2

The law of conservation of momentum states that if a body A of mass m1 and initial velocity u1 collides with a body B of mass m2 and initial velocity u2 , then after collision their final velocities will be v1 and v2 respectively:
(m1 x u1) + (m2 x u2) = (m1 x v1) + (m2 x v2) = constant

The question:
As i) the law is an axiom, hence must be true,
ii) the weight of neither heavy freight train nor tiny insect did change,
iii) speed of insect, above ground was initially about zero,
iv) speed of insect afterwards is = speed of train,
v) there was a time that insect had the speed zero
vi) then momentum = m(insect) x (speed = 0) = 0 =? momentum(train) is zero too?
vii) there is a first moment that insect & train have the same speed,
viii) hence speed v of both train and insect must have been zero at one moment?.
________________________________________________________________________________________________________________
EDITED: insect flies a tiny bit into the direction of the train

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Greetings,
Tommie

3dan EGF (AGA no 13477) || Tommie on KGS: 'June'|| DGS: 'Zhi Laohu' 纸老虎 = 'paper tiger' || Senseis : http://senseis.xmp.net/?tderz ||
ENFP (MBTI) - 'Find your own style within the Fundamentals of Go! '