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Questions tagged [physics]

A puzzle relating to physical equations or physical principles such as energy, entropy, and classical/quantum mechanics. General physics questions are off-topic here but can usually be asked at Physics Stack Exchange.

9
votes
1answer
298 views

The Lazy Laser Physicist: Part 2

The Lazy Laser Physicist is quite shocked about what happened to his setup over night: Almost all of his mirrors were taken away, but some other things have been put on his table. Besides these there ...
14
votes
7answers
3k views

The Lazy Laser Physicist

You have a setup like in the image above. But it seems like detector A does some weird things. You should better check it with detector B. What is the minimum number of mirrors you have to move (...
10
votes
4answers
2k views

Where does the emperor sit and why the earplugs?

The Emperor is annoyed that the crowd routinely chant out of step at the Empire's largest circular amphitheatre. For example, they are supposed to shout phrases in unison such as "Hail to the Emperor, ...
14
votes
4answers
553 views

Balancing Balls

I have a disk with 6 equally spaced dents around the edge. The disk balances on the center point. I want to place marbles around the edge so that it stays balanced. There are four ways that this can ...
7
votes
7answers
1k views

Perpetual Motion Machine [closed]

An engineer tests a new generator by attaching it to a motor-powered cart. The generator operates such that the cart's batteries charge when the cart's wheels turn. Assume the following true ...
20
votes
7answers
2k views

Making a physicist

Materials: CV step-up transformer with coil ratio 1:5 Method: Apply the CV to the primary coil and spin it. Result: A physicist is output. Who? Hint 1: Hint 2:
4
votes
1answer
146 views

An Incorrect Summary of a Twenty-Two Day Tour

After a long but rewarding life in an office cubicle, Sally the office worker became Sally the retiree. Feeling unfulfilled, and with ancestors who had served admirably in the Navy, Sally the retiree ...
-1
votes
1answer
203 views

Fuzzy's Fizzy Dilemma

Fuzzy the Fuzzball's friends was going to the Fuzzball Festival, and of course he went along. While there, he saw the most curious display. The booth was displaying brand new types of Fuzz. There was ...
10
votes
6answers
1k views

In which direction does the water flow?

There is a hard metallic pipe in your dark wine chamber. You hear the water flowing slowly in the pipe but you cannot understand in which direction that water flows since it is a closed system. ...
23
votes
15answers
11k views

Separate the milk!

You have a jug of milk and a jug of water. You must empty both jugs into a nine gallon barrel. You must be able to: Differentiate between the milk and the water Separate the milk from the water You ...
3
votes
2answers
254 views

Packing (cooking equipment) for Mars

Heading to Mars tomorrow, and I want to make sure I can still make my famous bean soup. Ordinarily I just cook it in a pot, but I remembered that beans are hard to cook at high altitudes, and Mars is ...
11
votes
5answers
745 views

More than equilibrium

Assume you have 2 identical metal cubes, the only difference being their temperatures $T_1 = 0 \, \text{°C}$, $T_2 = 100 \, \text{°C}$: The task is now to transfer as much heat as possible to the ...
-1
votes
3answers
222 views

Untwisting a long rope

Have you noticed that if you take your mouse and hang it from the end it will start to twist until it becomes untwisted? My puzzle is this: If you have a really long rope and not enough vertical ...
13
votes
10answers
2k views

Frequentists be damned! Design an evil coin to prove a point [closed]

The frequentists' definition of a "fair coin" is a coin that, tossed a million times, converges toward an equal number of heads and tails. But what is meant by converges? We might imagine a plot of ...
19
votes
4answers
2k views

Martin Gardner's “The Twiddled Bolts”

This is a puzzle of Martin Gardner, taken verbatim from My Best Mathematical and Logic Puzzles: Two identical bolts are placed together so their grooves intermesh. If you move the bolts around each ...
9
votes
2answers
411 views

A big logical mess

I found a drawing under a stack of books in my house. It looked like a logical circuit diagram, so I decided to make it. I assumed that I was allowed to put anything in the boxes with the question ...
3
votes
1answer
216 views

Figure out the ? in the figure below

Here is the link to the puzzle
-3
votes
1answer
200 views

Everyone is attracted to me! [closed]

Everyone in the world is attracted to me even though I'm the most abhorrent and repulsive creature to roam the earth. Though I am human, exploit no human weakness, and there are much more suitable ...
0
votes
2answers
184 views

First I'm the parent and then I'm the daughter

A simple, one sentence riddle which I'm confident you'll know when you have the correct answer. First I'm the parent, but I lose He and some energy, then become the daughter. What does this riddle ...
1
vote
2answers
311 views

Colliding Hang Balls [closed]

Two identical balls are attached at the ends of inelastic and very light string. Hanging on a fixed friction less pulley, one is pulled higher so that it is at right angle with the other ball. If ...
1
vote
2answers
191 views

Identifying Ancient Artifact

You are a group of archaeologists and scientists investigating an ancient cave. You set up and verify a presurization system at the entrance, which you can use to suck all the air out of the room, or ...
11
votes
1answer
690 views

Meeting of 8 flies [closed]

In the following diagram 8 flies are located at the corners of a cubic room, 10 feet on each side. At time 0 each fly starts to fly towards its neighbor fly as indicated in the diagram. Their speed of ...
4
votes
4answers
1k views

The largest and smallest value with 4 resistors

In physics, a resistor is an electrical component that inhibits current. We represent its ability to inhibit current with a value called its resistance, represented with $R$. ($R$ is always positive.) ...
6
votes
6answers
543 views

Misguided testing

Tom's job was to test light sensors for the Navy. He would mount 4 sensors at a time in a test circuit, then shine a light at them and measure the output. "Sensor #157 is clearly the best," Tom ...
0
votes
2answers
107 views

The driver and the chickens

In a sealed container van, there are 5 chicken cages with a chicken each. The driver has to cross a dilapidated bridge by jumping over it. If he can minimize the weight of his truck by even just 3 ...
5
votes
1answer
174 views

The Random Rube Goldberg Messup

You just finished making pretty cool Rube Goldberg machine. You test it. In a part of the machine that utilizes dominos, (where each domino is 1.65 times bigger than the one before) one domino didn't ...
4
votes
1answer
236 views

Game of Billiards: Kill the Planets Too

Below is a $8 \enspace \text{ft} \times 4 \enspace \text{ft}$ $\enspace (=243.84 \enspace \text{cm} \times 121.92 \enspace \text{cm})$ billiard table, with a perfectly flat playing surface. The ...
9
votes
4answers
1k views

Use a circuit to multiply two resistances

Given two resistors of unknown resistances and an infinite supply of wires and other resistors, create a circuit using multiple series and parallel combinations such that the effective resistance of ...
6
votes
9answers
5k views

Color of the bear

A bear fell from a height of $10$ metres from ground. It reached ground in $\sqrt2$ seconds. But somehow, it didn’t get hurt. What is the colour of the bear? Note : There is no ...
1
vote
4answers
2k views

Sudden braking on the highway [closed]

Have you ever noticed how, on a highway in conditions of heavy traffic, whenever you have to brake for any reason, the braking turns out to be sudden and hard? The same does not seem to happen on ...
3
votes
2answers
342 views

Hot Tea and an Unexpected Visitor

You're enjoying a Saturday morning, making a cup of tea to start the day. Just as you've finished pouring the boiling water into your teacup, you hear a knock at the door. If you like your tea with ...
14
votes
3answers
2k views

Bars in the river

There is a brick of gold and a brick of iron in a boat on a lake (both 10 inch blocks), if they are both dropped into the water which will make the water level higher? Edit we can assume its a very ...
5
votes
4answers
824 views

Dungeon Crawler - Final Level

You are the protagonist in a game designed by NeedAName Inc. Proceed through the levels using your video game knowledge to solve the puzzles therein. Solve all levels and beat the game! Level 4: ...
-2
votes
1answer
201 views

What is heavier?

Remark: Because of the comments I decided to drop the made up story, to remove any ambiguities. You have a balance scale. On one side of the scale you put an $1kg$ cube made of iron, on the other ...
0
votes
2answers
574 views

Make a glass sit above two other glasses using only a regular banknote [closed]

On a table there are three cups and one banknote (a dollar bill will do). These are the only objects you may use, with the goal of placing one of the cups, upright, above the other two, without any ...
52
votes
12answers
12k views

Is it always possible to balance a 4-legged table?

A perfectly symmetrical small 4-legged table is standing in a large room with a continuous but uneven floor. Is it always possible to position the table in such a way that it doesn't wobble, i.e. all ...
19
votes
4answers
2k views

How many boxes are conductors?

The Question (Some knowledge of potential difference, resistor combinations, etc. required) You have 1000 boxes. Some (or none) of them are conductors (of negligible resistance). The rest are ...
13
votes
4answers
940 views

Aquaman's Revenge!

After you posted mean things online about Aquaman, he found out where you lived and kidnapped you (using his awesome aqua-powers), taking you to his super-secret aqua-lair. He has placed you in a room ...
2
votes
2answers
326 views

Which candidate is most washed up?

Donovan Clump and Hermione Timmon are political candidates in the electoral race for "Most Thankless Job in Modern History". Both candidates set out into the wilderness at the same time. Rains are ...
7
votes
3answers
675 views

Memento Vivere; Momentum Mori

Bob, a budding physicist, is sitting on a swivel chair at rest, holding out a large motorized flywheel in front of him. The wheel is oriented parallel to the ground. Bob's swivel chair is a magical, ...
-3
votes
2answers
515 views

Why is my desk wet? [closed]

A brewing cup of tea sits on my desk. Full of water and milk When I put the cup down I was very careful not to spill a drop When I came back 2 minutes later, my desk was damp with hot tea. Why???
8
votes
2answers
365 views

Bracing a Flexible Grid

Suppose that you build an $n$ by $n$ grid out of metal rods, joined at their ends in such a way that they can rotate about the joints. Below is the grid when $n=3$, along with an illustration of its ...
5
votes
5answers
1k views

Faster than the speed of light [closed]

(I am not the origin poster of this question but I have failed to provide the references) A scientist claims that he found the way to break the speed of light barrier - faster than the speed of ...
9
votes
4answers
2k views

Fisherman boat and sea level

A fisherman rowing his boat on a very small lake throws his anchor into the water. Does the water level of the lake rise, fall or stay the same?
18
votes
4answers
6k views

A semi truck weighing exactly 10,000 pounds

A semi truck weighing exactly 10,000 pounds gets onto a bridge that is 100 miles long. The bridge's actual weight limit (not the posted limit) is exactly 10,000 pounds; any more will break the bridge. ...
4
votes
4answers
1k views

Find the magnet among the two rods

Dilemma You are taken to a dark room and given two thin long rods - 30 cm long and 1 cm thick. One of them is a permanent magnet and the other is pure iron which is not magnetized. Both of them are ...
1
vote
4answers
1k views

The Twins with a Different Age

Warning: To answer this riddle you need to have a thorough understanding of how time works. Two twins were born during the same year, on the same month, and the same day, exactly 10 minutes apart. ...