Another Physics Problem!

[Sidoh]

You have two disks.  You want to put them at the same height on a ramp and release them at the same time.  Which will get to the bottom faster?

No guessing, you have to prove your answer with MATH! :)



[ Just a hint -- the weight of the disks in this problem is not very affecting of the differences in the times the two disks cross the finish line.  It's something else. ]

[iago]

Wow, negative weights! Crazy :)

Correct me if I'm wrong, but didn't some famous guy roll various things with a different masses/densities down a ramp, and drop them off a building, and discovered that stuff falls the same speed no matter how heavy/light/dense it is (as long as wind resistance doesn't count)? 

So, unless you want to calculate wind resistance, they should get there at the same time. 

If you DO want to use wind resistance, then the solid one will, because having a hole in the hollow one will create drag. 

Of course, maybe there's some totally other explanation.  But I don't see how this case would be any different from the orange/bowling ball..

[Sidoh]

Those are dashes, silly!

And it is correct that the acceleration due to gravity is constant throughout all objects, if air resistance is ignored.  We may ignore air resistance in this problem and get very similar results.

One of the disks will finish first by a long shot (~0.5s, it's pretty obvious which one wins), but why?

To clarify, I'm going to give the objects a substance so it's less confusing.

Disk #1 is a PVC pipe -- it's hollow, but pretty dense.

Disk #2 is a circular section of cork board.  It's solid, so it weighs about the same as the PVC pipe.

[Sidoh]

Since there was another Physics problem broght up, I figured I should bump this one!

I demonstrated the tequnique (or at least the very general concept) of what you need to know to solve this.

Subliminal Message - Rotational Kinetic Energy

[Towelie]

thats not very subliminal :-)

[Sidoh]

x86] link=topic=3832.msg43220#msg43220 date=1134003732]
thats not very subliminal :-)

SOLLLVEE ITT. :(

[Towelie]

ok, give me a year, I'll be taking physics at that time ;D

[deadly7]

Ha, I'm learning physics @ home!

[Sidoh]

Ha, I'm learning physics @ home!

Anyone can.

[deadly7]

Yeah, but you need like.. textbooks to do so, I'd imagine.  I robbed Barnes and Noble the other day for some physics books.

[Sidoh]

Yeah, but you need like.. textbooks to do so, I'd imagine.  I robbed Barnes and Noble the other day for some physics books.

You imagine falsely.  http://en.wikipedia.org and http://www.google.com are all the tools you need.

[deadly7]

It's easier with books, for me, I can't concentrate on a computer cause forums and AIM exist. :P

[Sidoh]

It's easier with books, for me, I can't concentrate on a computer cause forums and AIM exist. :P

Oh one of little concentration...

[deadly7]

Hehehe. I'll turn on my monitor to change the song.
And then I"ll end up turning on programs, etcetcetc and then bam I'm stuck and not learning.