***---Physics---***

[mykg4orce]

i need help to figure this out...

A 75kg petty theif wants to escape from a third-story jail window. Unfortunately, a makeshift rope made of sheets tied together can support a mass only 50kg. How might the theif use this "rope" to escape? Give quantitative answer.

[parksie]

Too tired to give numbers...but how about doubling the sheet over?

[mykg4orce]

you mean now it can support 100kg?

[CyberSurfer]

hehe! Nice one, Behemoth!

[Active]

Originally posted by mykg4orce
i need help to figure this out...

A 75kg petty theif wants to escape from a third-story jail window. Unfortunately, a makeshift rope made of sheets tied together can support a mass only 50kg. How might the theif use this "rope" to escape? Give quantitative answer.

Well ..it is not common to express a person's mass but
however we express a persons weight...

this 75kg is actually his weight !

and since the rope can support a mass of 50kg
it can actually withstand a weight(force) of m *g

= 50 * 9.81 N (or Kgf)

= 490.5 N or 490.5kg Weight

therefore the thief can escape...

[paulw]

Errr. Not quite since a person's weight is their mass at 1G since this thief is on earth gravity will be close to 1G and therefore his mass will be at least 60Kg (even at the top of Everest). The rope cannot support that mass directly.

So the answer is - move the jail to the moon.

Cheers,

P.

[HarryW]

Double it over, climb down half way and then just drop. Or make a really big air-filled pillow out of the sheets and jump onto it

[Active]

[This post deleted. See my Post below ]

[parksie]

Mass is measured in kilograms, and shows how much of you there is -- this does not change.
So Active has a mass of 55kg.

Weight is measured in Newtons, and shows the downward force of that mass, which is represented by g * the mass.

On Earth, g = 9.81ms^-2, so Active's weight is 539.55N.

[HarryW]

I think you're missing something - weight is measured in Newtons (N) and mass is measured in kilograms (kg). The problem states that there is a theif of 75kg. It is not stated whether this is mass or weight but since the units are kilograms we can safely assume it's the mass.

Also, the acceleration due to gravity (~9.8 m/s²) is g (little G), whereas G (big G) is the gravitational constant.

If the theif has a mass of 75 kg, then he has a weight of about 735 N (on Earth at sea level at least).

[HarryW]

Hmm looks like I should have typed faster

[Active]

oooopss Messed it up again..

1G is the unit of acceleration ie...

9.81 m/sec² = 1G

There fore weight of a Person having a mass 2 kg is
weighing (2 * 9.81 ) = 19.62 Newton or 2Kg Weight

What we measure using devices like weighing machine
is not a persons mass but a person's Kg weight. <--

There for the Persons mass is actually 75 Kg
and his weight therfore is 75 kg Weight = 75 *9.81 N

***
My Weight for example is 55 Kg weight = 55 *9.81 N
My mass therefore is 55 kg

Sorry... !!!
Parksie and harry are right ..

[Active]

Originally posted by HarryW
Also, the acceleration due to gravity (~9.8 m/s²) is g (little G), whereas G (big G) is the gravitational constant.

We did not mean the Universal Gravitational Constant..

But we meant the G-Force...

1G force is the force experienced by a mass due to earth's g

Usually centrifugal forces are expressed in terms of G force. ..example 2G force 3G force etc....


For example in roller coaster rides...at the top most point
you will sometimes experience up to 4G force...
That is the thrill factor..

[parksie]

It's still g-force

[Active]

Yes u can use 1g 2g etc... but the most common form
is to use capitals.... Like 1G 2G etc..

But it does not in any way mean... the Universal gravitational Constant( Heck..there are a lot of G's)

Look this Brittanica link..

They use capital G

http://www.britannica.com/eb/article?eu=22442

[parksie]

Fair enough

[Active]

Originally posted by parksie
Mass is measured in kilograms, and shows how much of you there is -- this does not change.

This might be interesting...

mass is constant for even a moving body in Newtonian
approach..But it Einstein's Relativistic model ...

any body having inertial mass and in motion (actually no body in the universe is at absolute rest) gets an
increase in Mass. This increase is almost negligible at
speeds we experience..

but at 10 percent of the speed of light the body's mass
is 0.5% more than normal and at 90% of C the body will
have more than twice it's normal mass.

[parksie]

Technically you're correct here, however it makes very little difference. As you slow down your mass will decrease again so there is no net difference

All that will happen is you'll just increase in mass in accordance with the kinetic energy gained

[Active]

Ya...But the fact is Mass varies with time..
{If you believe in Relativity Principles }

[parksie]

I'm not disputing the fact that it can change, it's just under normal circumstances it doesn't.

And please don't say that it'll change even if you're only walking along

[Arbiter]

Bollocks to all this Universal Sanitation Constant or whatever, it's only a three story drop, why doesn't he just tie the sheets around his ankles to limit damage and leap out of the bloody window.

And, more importantly, why are we assisting a thief in his escape anyway?

Do we have no morals?!?!?!?

[HarryW]

I think you know the answer to that one.

[Active]

Originally posted by parksie
I'm not disputing the fact that it can change, it's just under normal circumstances it doesn't.

And please don't say that it'll change even if you're only walking along

This is the fun part of it...
You think you are walking and so you are slow moving..???

Okay I am a Person in another frame
standing above the north pole and to me you seem to
move at nearly the rotational velocity of earth.

Even better I stand above the centre of the sun and
I see that you are moving with the very high earth's revolving velocity that you seem to revolve around the sun in 1 year !!!

Now if I stand Just outside milky way - our own Galxy
you are moving at a terrible speed.....

[HarryW]

Well that's why it's called relativity.