What’s the radius of the circle?

[Cooldude]

OK folks…. Crack this puzzle.

In the drawing below is a square whose sides are perfectly tangential to the circle inside it. The rectangle on the top left of the circle has the dimensions 5 x 10 (Dimensions in centimetres as shown in drawing).

So what’s the radius of the Circle in centimetres?

[dhurandhar]

Let me help people get started....

work with a triangle whose sides are "r - 10" and "r - 5" respectively and vertex the origin of the circle...of course r = radius of the circle

[dhurandhar]

i am surprised people haven't found the answer yet

one more hint...similarity of triangles...think what can be a good candidate for the second triangle

[rameshp]

Originally Posted by dhurandhar

i am surprised people haven't found the answer yet

one more hint...similarity of triangles...think what can be a good candidate for the second triangle

i already got that dhruu pai. not interested, thats all. thanks for initial idea though in ur post 1.

[GunsNRoses]

I know how to solve it. The same thing was from a puzzle by Henry Ernest Dudney (I used to have a book of his math puzzles a long time ago). The puzzle was more of a description though and didn't have an illustration like you put there.

[Napolean]

No answers and no hints please...I am solving it.Thanks.

[Cooldude]

Originally Posted by GunsNRoses

I know how to solve it. The same thing was from a puzzle by Henry Ernest Dudney (I used to have a book of his math puzzles a long time ago). The puzzle was more of a description though and didn't have an illustration like you put there.

I made the simple drawing in AutoCad... GNR... to illustrate it better..

Originally Posted by Napolean

No answers and no hints please...I am solving it.Thanks.

OK Naps.... Take your time... Dhuru's hint is right..

Any eCharchan who solves this, please post with an image (preferably AutoCad) to show your answer. Thanks.

[ShivSainik]

KYa CD bhai....Subhe subhe dimag lagane ke liye majboor kiya

Good puzzle Found the answer

[2gud]

Answer: R = 25

Too simple for 2gud

[2gud]

Originally Posted by 2gud

Answer: R = 25

Too simple for 2gud

CD bhai as per your request:

Solve the Pythogoras for the right angled triangle with sides R, R-10 and R-5

(R-5)^2 + (R-10)^2 = R^2

R = 5 or 25.

R can only be 25 as the other answer is untenable.

Cooldude please turn up with better questions than that of elementary maths! UMA ben in the past had some really good puzzles.

[ShivSainik]

Here is somewhat difficult puzzle....

For intelligent Echarchans like 2gud.......(Simple for physics gurus but difficult for normal guys)

What is the weight of the Moon?

(Dont use google !!!)

[Cooldude]

Originally Posted by 2gud

CD bhai as per your request:

Solve the Pythogoras for the right angled triangle with sides R, R-10 and R-5

(R-5)^2 + (R-10)^2 = R^2

R = 5 or 25.

R can only be 25 as the other answer is untenable.

Cooldude please turn up with better questions than that of elementary maths! UMA ben in the past had some really good puzzles.

Thanks for the solution 2Gud...

The answer is the Pythagoras theorom followed by factorising the quadratic equation.

(R-5)^2 + (R-10)^2 = R^2

R = 25

Below is my drawing for the solution:

[echarcha]

Originally Posted by ShivSainik

Here is somewhat difficult puzzle....

For intelligent Echarchans like 2gud.......(Simple for physics gurus but difficult for normal guys)

What is the weight of the Moon?

(Dont use google !!!)

I think the moon is baout 1/80 th of the earth.. I hope my memory from Geography class serves me right..

[ShivSainik]

Originally Posted by echarcha

I think the moon is baout 1/80 th of the earth.. I hope my memory from Geography class serves me right..

Yes... But what your are talking about is MASS and not weight...

[2gud]

Originally Posted by ShivSainik

Here is somewhat difficult puzzle....

For intelligent Echarchans like 2gud.......(Simple for physics gurus but difficult for normal guys)

What is the weight of the Moon?

(Dont use google !!!)

Weight of moon may be misleading, as that would need you to define where - On the earth surface or moons orbit?

I take it that you mean calculating mass of the moon using a simple Physics technique?

I know from my college days that this problem is tricky as the acceleration of a body does not depend on the mass of the accelerating body. In other words mass of moon cannot be calculated by equating centrifugal acceleration on moon due to its rotation to gravitational acceleration of earth on moon. Though we can calculate earth's mass by this technique.

Similarly we need to have a satellite of known mass put into orbit around moon, having known its period of rotation and distance from moon's center, we can calculate mass of the moon.

Other way (which is the way mass of moon was first determined) is to find the location of center of mass of earth & moon system (which is inside earth), this along with other known values (mass of earth, time period of earth and moons rotation around this center, we can calculate moon's mass. But finding out the location of center of mass of earth and moon system is complex process. I hope I can point you to some sources on how they calculated it.