Ask Ravi

[4swrds]

Originally posted by cultclassic+Sep 13 2006, 08:12 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (cultclassic @ Sep 13 2006, 08:12 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-4swrds@Sep 13 2006, 04:32 PM
my grandparents use wooden sticks to brush their teeth...

....sooo wierd...

:lol: Mango tree right? My grandfather did that too... He used to make me climb the mango tree to get fresh sticks. Which caused conversations like this, with neighbors:

what are you doing up the tree? don't you have school?
grampa needs to brush!
Oh.
WHAT??? WHO??

Never used toothpaste... he had perfect set of teeth when he was like 90! [/b][/quote]
:lol: ...Ha! thats awesome, I think I should start using thoses sticks....

 

[4swrds]

Originally posted by leone@Sep 13 2006, 11:11 PM
In the meantime, what do you suggest, Physics for Dummies or Complete Idiot's Guide to Physics? :lol: I'm not kidding!

Id say the complete idiots guide to physics, cause it sounds cooler...."I aint no dummy, Im a complete idiot! B) "

 

[dascoot]

Ok speaking of physics, Ravi or possibly Leone The Physics Goddess, I have a question about the properties of glass, or more specifically TEMPERED glass patio tables.

K. I went to my dad's house to drive him to his post-op therapy and he's like "Hey come out here and take a look at this." Their glass patio table was shattered, like COMPLETELY shattered, and he said it just happened and he couldn't figure out how.

This is what it looked like. The part you CAN'T see is that there's still glass clinging to the corners, trapped in the metal frame part. Those corner pieces are completely shattered too.

We looked everywhere but there were no rocks or anything that coulda landed on it to break it. There's no way someone coulda sneaked onto the patio and done it without the dogs goin apeshit (nor could we think of any reason for someone to do it). Besides, if it had been hit with something there woulda been spiderweb cracks in a radial pattern, and as shown by the state of the glass still in the corners of the metal frame, this table had been shattered across its entire length before it ever fell through the frame to the ground.

So my question is HOW THE FUCK CAN THIS HAPPEN TO TEMPERED GLASS? I'm totally baffled, and the fact that I had a ghosty encounter at my own house at approximately the same time this was happening at my dad's house is sorta creepin me out. :blink:

 

[4swrds]

Originally posted by dascoot@Oct 4 2006, 06:42 PM
Ok speaking of physics, Ravi or possibly Leone The Physics Goddess, I have a question about the properties of glass, or more specifically TEMPERED glass patio tables.

K. I went to my dad's house to drive him to his post-op therapy and he's like "Hey come out here and take a look at this." Their glass patio table was shattered, like COMPLETELY shattered, and he said it just happened and he couldn't figure out how.

This is what it looked like. The part you CAN'T see is that there's still glass clinging to the corners, trapped in the metal frame part. Those corner pieces are completely shattered too.

We looked everywhere but there were no rocks or anything that coulda landed on it to break it. There's no way someone coulda sneaked onto the patio and done it without the dogs goin apeshit (nor could we think of any reason for someone to do it). Besides, if it had been hit with something there woulda been spiderweb cracks in a radial pattern, and as shown by the state of the glass still in the corners of the metal frame, this table had been shattered across its entire length before it ever fell through the frame to the ground.

So my question is HOW THE FUCK CAN THIS HAPPEN TO TEMPERED GLASS? I'm totally baffled, and the fact that I had a ghosty encounter at my own house at approximately the same time this was happening at my dad's house is sorta creepin me out. :blink:

:blink: ....yep...its definitely ghosts....or ninjas...or ghost ninjas!

 

[leone]

Originally posted by dascoot@Oct 4 2006, 06:42 PM
Leone The Physics Goddess

:lol: Lies!


Did you guys have a temperature change around the time that happened?

 

[cultclassic]

Originally posted by leone+Oct 4 2006, 08:28 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (leone @ Oct 4 2006, 08:28 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-dascoot@Oct 4 2006, 06:42 PM
Leone The Physics Goddess

:lol: Lies!


Did you guys have a temperature change around the time that happened? [/b][/quote]
Leone Hawking!!! *bows down* B)

Yeah that could do it, If the glass was tightly held inside the metal frame, beacuse metal expands/contracts more than glass.

 

[cultclassic]

are there any fat singing ladies in the neighborhood? :lol:

 

[leone]

:lol: :lol:


I was thinking that something hit and damaged the glass a while back and then the temperature changed and the glass went boom! :leela:

 

[dascoot]

The only fat lady around is me, and no, no temperature change. It's been in the 90's since pretty much February.

 

[leone]

Someone dropped a giant block of ice out of a plane? h34r:

 

[dascoot]

:lol: Then the fucker evaporated quickly.

 

[leone]

Liquid nitrogen! :leela:

 

[leone]

Okay, so I have the answers, I just don't know how to do it. Help.

The position (vector) r of a particle moving in an xy plane is given by (vector) r=(2.00t^3 - 5.00t)i + 96.00 - 7.00t^4)j, with (vector) r in meters and t in seconds. In unit-vector notation, calculate a.) vector r, b.) vector V, and c.) vector a for t=2.00 s.

 

[cultclassic]

Originally posted by leone@Oct 17 2006, 09:44 PM
Okay, so I have the answers, I just don't know how to do it. Help.

The position (vector) r of a particle moving in an xy plane is given by (vector) r=(2.00t^3 - 5.00t)i + 96.00 - 7.00t^4)j, with (vector) r in meters and t in seconds. In unit-vector notation, calculate a.) vector r, b.) vector V, and c.) vector a for t=2.00 s.

r=(2.00t^3 - 5.00t)i + 96.00 - 7.00t^4)j
??
Leoney did you miss a starting parenthesis?
is it
r=(2.00t^3 - 5.00t)i + 96.00 - (7.00t^4)j
or
r=(2.00t^3 - 5.00t)i + (96.00 - 7.00t^4)j

either way:

a) plug the values for t=2 and calculate..

b ) V=dr/dt, so differentiate r WRT t, then plug in the values for t

c) differentiate again, WRT t, and plug the values.

 

[leone]

Originally posted by cultclassic@Oct 17 2006, 10:17 PM
Leoney did you miss a starting parenthesis?

Sure did! :duh: It's suppose to be vector r= (2.00t^3 - 5.00t)i + (6.00 - 7.00t^4)j

Thank you. :wub:

But for a.) how do you know that you should plug in 2? Is there a rule or something because (in calc) after differentiating, I just leave it alone. Then again, we're doing that with trig functions and natural logs, so maybe that comes later...?

 

[Caren H]

I feel like a total moron right now... :mellow:

 

[cultclassic]

Originally posted by leone@Oct 17 2006, 11:06 PM
a.) how do you know that you should plug in 2? Is there a rule or something because (in calc) after differentiating, I just leave it alone.

because:
the formula
r= (2.00t^3 - 5.00t)i + (6.00 - 7.00t^4)j
defines the position of a point, defined by the tip of a vector r, on the (i,j) plane. That is: if you know the value of time t, in seconds, this formula tells you where the point lies, (it's i & j values) at that particular instance of time...
since you know the position formula, you can find the velocity formula by differenting it: that is, whenyou differentiate the original formula, with respect to time, you get a new formula which gives you the VELOCITY of the point r at any time t.
differentiate it again, you get the ACCELERATION, of the point t, at any value of time t.

now to answer your question: when you do calc, you aim to find these different formulas. but ultimately, engineers use these formulae to calculate real-world values, of velocity/speed, acceleration/gforce etc... that's when you plug the parameters, like, time, in this case, into the formula to find the resulting value: position, velocity, acceleration whatever... that's what they're asking herre.

 

[leone]

So if they didn't give you, wait! :banghead: Okay, I'm an idiot. When I read the question, thought that t=2 applied only in part c. :duh: :duh:

 

[cultclassic]

*note to self* Well, Confucious, :duh: :duh: all you had to say was t=2 applies to a, b and c Respect the Goddesses' ATHORITAY!!! :duh:

 

[leone]

:lol: I won't tell anyone about this if you won't.