Phys

[101dalmatians]

Ugh
I doubled my score in chem when comparing it with phys
nd im learning pap for both
ugh
omg
How? How do u do phys w/out relying on the book?
I mean I watch lectures # from MIT and go to khanacademy but they dont helpme that much...
I at least wanna 50! :(

[smeag]

Can someone please explain the following problem in detail ?

Two identical point charges are placed diagonally on opposite corners of a square that is .750 m on each side.
Each charge is 2.5 x 10^-6 C. How much work is done by the electric force as one of the charges is moved to an empty corner of the square?

*Please explain your process*

Thank you very much!! :)

[sxk1693]

Ok, let me try. Can you post the answer too.

My first step would be to find the force vector.

Let me find the Magnitude first:

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[sxk1693]

The Force vector is equal to .050 J at 45 degrees.

Lets find the Horizontal component(Actually you can use the vertical component for this problem also since the problem stated ANY empty corner).

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[unparseable or potentially dangerous latex formula] Store that value in your calculator.

[sxk1693]

Now you need to find the Work.

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In this case d is the distance needed for a charge to travel to an empty corner, so it is just .750 m.

So,

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[darksaber21]

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[darksaber21]

[darksaber21]

Calculus Method:
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Now just plug in values to get the same answer.

[darksaber21]

[smeag]

Thanks very much!!! oh and the answer was -2.2 x 10 ^ -2 J

[101dalmatians]

ok so i guess sxk1693's physics fails again...
but its ok
at least u try (to get it wrong :P)
me - I just skip those qs... I get my 2pts back!

[smeag]

Hi, can you guys please give me a basic idea of what to do on the following problem?

A train traveling at 38.5 m/s is approaching a crossing where a person is standing next to the track. The frequency of the train whistle is 512 Hz when the train is not moving.
What frequency will the person hear as the train approaches if the speed of sound is 343 m/s?

Thank you for helping!

[darksaber21]

Doppler Effect:

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So:

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[qwerty123]

@darksaber21, how do you know when to use the plus and when to use minus?

EDIT: Never Mind.

[sxk1693]

[sxk1693]

AND... My latex is an utter failure.

At least there is an explanation for the top and bottom signs. Just look at Darksabers post for the formula.

[sxk1693]

Where in the world did the 39 come from???

[darksaber21]

For some reason for this latex, using apostrophe for prime is incorrect, and you must use the code [^\prime] without the brackets to get the prime symbol, as such:
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I meant to explain the signs, but I considered it something you could figure out on your own. I thought you could retain it better if you thought about some parts of it now with help rather than later alone. But regardless, there you go.

[smeag]

A capacitor with capacitance C is charge to a voltage V and then connected across a resistor R. What is the equation for the energy stored in the capacitor as
a function of t in terms of the given quantities?

Please explain and thank you!

[sxk1693]

42

[sxk1693]

BTW 42=IDK and Someone else can probably help you

[007math]

[darksaber21]

You pretty much did, and that is usually the more easier equation to derive.

However, that equation only works if there is one capacitor connected to one resistor connected to one battery. Otherwise, you would have to tweak the equation a bit.

You end up with the same equation either way, so I'm going to use the discharging rate (when there isn't a battery), mainly since the question does imply that there is no battery (I think)

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Since [unparseable or potentially dangerous latex formula]

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Since [unparseable or potentially dangerous latex formula]

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[smeag]

Ok, does anybody know if physics C is being tested on the science tests? My entire physics experience has come from the giancoli physics book (non-calculus based). However, there are a few problems that appear on tests that are not covered in my textbook...

Also, what should I do when I try to open the tmsca science tests for 2010 district and invitationals? I even tried saving them but a message came saying "There was a problem reading this document"

[darksaber21]

Ummm, physics c is actually never tested (as c is a calculus-based course), so your textbook should suffice. It wouldn't hurt knowing some calculus formulas anyhow (as you could derive your own, but that might be too late to learn at this point I'm afraid.)
There are some concepts covered in c that isn't covered in b (such as angular momentum and moment of inertia), but again your textbook should cover it, if not the basic formulas for it.