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Questions tagged [physics]

A puzzle relating to physics equations or physical principles such as energy, entropy, and classical/quantum mechanics.

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 our sister site Physics Stack Exchange.

97 questions
32
votes
8 answers

Pulling the rope with one hand is as heavy as with two hands?

There is this box, having two holes, and the ropes going through each of them. I try to pull the left rope with my left hand... And it's heavy... Then I try to pull the right rope with my right hand... It's also heavy, as heavy as before. Ok so...…
athin
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17
votes
3 answers

A pencil in a beaker of water

You have a beaker containing 100ml of (slightly salty) water, standing on a digital scale. The scale has been calibrated to the beaker so that it shows only the weight of the water, which is exactly 100.0 grams. The beaker is perfectly cylindrical,…
Jaap Scherphuis
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15
votes
3 answers

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 small and light boat. (feel free to change the…
Marco Geertsma
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11
votes
1 answer

Clever Collision Counting

A mass of 1,000,000kg is sliding in from the right on a friction-free, level surface. It has a perfectly elastic collision (collision 1) with a stationary 1kg mass. To the left of the 1kg mass is a wall and the 1kg mass bounces off the wall with…
Dr Xorile
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11
votes
6 answers

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. What could be the easiest way to find in which…
Oray
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9
votes
4 answers

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?
Maximin
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8
votes
7 answers

Perpetual Motion Machine

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 observations. Starting from a location, the cart…
1848
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7
votes
3 answers

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, 100% completely frictionless swivel chair, and…
COTO
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6
votes
1 answer

A very familiar object

I'm sure you all have held a common retractable, spring-loaded pen at least once, and that many of you have tried to make it jump vertically by first pushing it downward against a table to load the spring (and then a second time to release it). But…
The Footprint
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5
votes
1 answer

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 fall over, and your machine fails. You try again…
Xxoplechic
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4
votes
1 answer

Traffic lights in space

In a distant future, human beings are travelling between planets and even solar systems with ease. Their advanced technology allows them to drive their own space-cars, which have a cruising speed of 20% of the speed of light. Due to the increasing…
PKlumpp
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4
votes
4 answers

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 insulated with glass. They weigh the same. The…
Renae Lider
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4
votes
1 answer

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 cushions are removed for the sake of simplicity. You…
BaSzAt
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3
votes
3 answers

Two Identical Pistols Shot Simultaneously

Two identical pistols are shot at the same moment, one in Death Valley and the other the Schwarzwald Germany. Both of them are at targets 40 meters away. Which one hits its target earlier?
Anthony Trucano
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3
votes
1 answer

Figure out the ? in the figure below

Here is the link to the puzzle
alDiablo
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1
2