Jump to content

Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse


Member Since 05 Dec 2012
Offline Last Active May 21 2015 02:04 PM

#342152 Center of Gravity

Posted by TimeSpaceLightForce on 18 May 2015 - 03:18 PM

Lets see..

Spoiler for


Not like how I imagine it ( center of gravity in x-y-z symmetry). But that is better!


Spoiler for



  • -1

#342143 Center of Gravity

Posted by TimeSpaceLightForce on 15 May 2015 - 02:22 PM

This is a simple mechanics+ geometry puzzle..

I'm not sure if the "2015 MIT Mystery Hunt"  is a type of metapuzzle?

  • 0

#342140 Center of Gravity

Posted by TimeSpaceLightForce on 15 May 2015 - 04:02 AM

It does because the title is connected to the figure and the question..
The firgure are rectangles with elipse on top of one end.. no color, but common
sense tells us it represent an arrangement  of matchsticks that need to be modify
for higher symmetry..
You could see dozen solutions easily , Yet chosen the square cross..why not the 2x2 square? 
why not the tic-tac-toe? This is where you supposed start to wonder and recheck and 
reconsider everything.. or 'look inside the box'.

  • -1

#342133 Center of Gravity

Posted by TimeSpaceLightForce on 14 May 2015 - 09:35 AM

No, I would have no reason to consider the [placement of the] heads, because it is a matchsticks puzzle.


The matchsticks puzzles have never limited themselves to placement of the heads.  If you had wanted


that extra condition, then you are changing what kind of traditional puzzle this is and not announcing in


the rules.

Spoiler for

  • 0

#342129 Center of Gravity

Posted by TimeSpaceLightForce on 13 May 2015 - 10:21 AM

Incorrect, TimeSpaceLightForce.

In my explanation and diagram, I already showed that

Spoiler for

Check it again,perhaps you didnt considered the heads.. 

  • 0

#342125 Center of Gravity

Posted by TimeSpaceLightForce on 12 May 2015 - 03:04 PM

Spoiler for

  • 0

#342114 Center of Gravity

Posted by TimeSpaceLightForce on 10 May 2015 - 02:05 PM


3 match moves to balance symmetrically …Can you spot it?

  • 0

#341991 Sliding swing

Posted by TimeSpaceLightForce on 27 March 2015 - 07:44 PM

J  -- -- -- --o
Attached at ends of a one unit long and weightless cord  are two identical balls with a unit mass.
If the cord slides on hook J w/out friction.. How far can the higher ball can be pulled 
horizontally away  from J  ,so that when released it can hit  the lower ball?

  • 1

#341847 Time inside a box

Posted by TimeSpaceLightForce on 07 March 2015 - 06:13 PM


A merchant bought 4 watches from a craftsman .  On his way home he opened the box containing his purchase.
He realized that one is  telling a wrong time then notice one of them is not running while one of them is running
at different speed..only one always tell the right time. He returned  all the watches inside the box and brought
it back to the craftsman. When the box was opened for complaint the craftsman told the merchant that none of the
watches in that box tells the wrong time. The merchant believed him and went back home without replacement or
fixing of his purchase. Wearing the watch that always tell the right time ,when he got home the other  watches in
the box tells the right time.  Is there some explanation for this?

  • 1

#340562 Precast

Posted by TimeSpaceLightForce on 11 October 2014 - 10:06 AM

An engineer designed an open box mold for concrete mix pouring.
By cutting the standard 4" x 8" G.I. sheet with the right pattern he
then bend and weld  to produce maximized weight concrete blocks,
how was it done?  What is the precast volume?

  • 1

#340471 Pecular Spectra

Posted by TimeSpaceLightForce on 02 October 2014 - 10:07 PM

Three interstellar stations have observed a distant cluster of gas clouds
known as RGB-9. The stations are positioned at right angle with each
other. The photograph images captured by X,Y, & Z telescopes at the same
instant are having exactly the same configurations (see below). Some of
the gas clouds that are behind the other cloud emits a mixed spectrum..
How shall they construct the 3-D plot of the cluster?
rgb clouds.jpg

  • 1

#339558 Days of Dates

Posted by TimeSpaceLightForce on 17 August 2014 - 04:44 PM




What calendar year represent the figure above?

  • -1

#338948 nice dice

Posted by TimeSpaceLightForce on 07 July 2014 - 06:56 PM

nice dice.png
Everyday, six prisoners: numbered #1 #2 #3 #4 #5 #6 were randomly
locked-up inside six prison cells: [1] [2] [3] [4] [5] [6]...
No one have any information about the other locked-up prisoners.
They do not have any means of communications once inside the closed room.
During a dinner the warden offered the prisoners to participate in a game of chance. 
Anyone who can guess all the prisoner's # in every prison cell correctly 
shall be freed together with one of the other prisoners he selects. 
If the guess is wrong, both of them shall be hanged.
Anyone who wont guess will be hanged.
For accepting his challenge he would grant the prisoners request that 
one of the prison cells must contain a boxed dice to play and share.
Provided they can only send it once to other cell and received it once 
from other cell with the assistance of prison guard.
The six prisoners talked it over and all agreed to take the challenge.
On the next day they were all  locked-up with  blindfold ..
but they were all saved by the dice.
How can this be done? 

  • -1

#338618 Precision Watch

Posted by TimeSpaceLightForce on 12 June 2014 - 06:36 PM

At 12 minutes before 7 o'clock,
the watch has stopped and needed to be rewind.
But obviously the second hand is offset by +7 secs..
so it must be corrected before it runs again.
To adjust just rotate the second hand clockwise and
the hour hand will rotate likewise with the same angle.
Rotate the second hand counterclockwise and the
minute hand will rotate likewise with the same angle.
At what precise time of the watch should it be rewind?

  • 0

#338570 Pendulum Watch

Posted by TimeSpaceLightForce on 05 June 2014 - 09:54 PM

It is 12MN when  all the hands of this unusual watch rotates clockwise at proper speeds. 
But all the hands runs in opposite direction when they strike 12..like a pendulum.
What is the real time if it reads false as shown below ?

  • 1