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I have a handful of questions I need help with and figured compiling them in one thread was the best option. For the most part, i've added these because I just don't know where to start and can't figure it out at all. Here we go!

QUESTION ONE:

1. The problem statement, all variables and given/known data

A bar of copper with length 2.635m and a bar of Aluminum with length 2.628m are sitting at room temperature, T1 = 25C. At what temperature, T2, will the two have the same length?

The coefficient of thermal expansion of copper is 1.60x10-7 K^{-1}and of Aluminum is 2.25x10-7 K^{-1}.

2. Relevant equations

Linear Thermal Expansion: [tex]\Delta[/tex]L=[tex]\alpha[/tex]Lo[tex]\Delta[/tex]T

Lo = initial Length

3. The attempt at a solution

The given choice of answers are in C, so I figured I had to convert the thermal expansion coefficients to C^{-1}but wasn't quite sure how to do that.

K = C + 273

I figured the expansion would be Lo + [tex]\Delta[/tex]L

I set that eq. for the Al and Cu bars equal, subbing in the [tex]\Delta[/tex]L with the equation above. My answer is off though, and i'm not sure if it's a matter of because I didn't convert my per Kelvin to per Celsius or what. I think it's an algebra thing but maybe i'm way off.

QUESTION TWO:

1. The problem statement, all variables and given/known data

The sound level at a point X is 14db below the sound level at a point 1.0m from a point source. The distance from the source to point X is:

a) 2.0m

b) 25m

c) 5.0m

d) 20.2m

e) 4.0m

2. Relevant equations

Decibels = 10 log (I/Io)

Io = threshold of hearing = 1x10^{-12}W/m2

3. The attempt at a solution

I don't know where to start with this one!

QUESTION THREE:

1. The problem statement, all variables and given/known data

A heat conducting rod, 1.60m long, is made of an Al section, 0.90m long, and a Cu section, 0.70m long. Both sections have a cross sectional area of 0.0004m2. The Al end and the copper end are maintained at temperatures of 30C and 170C respectively. The thermal conductivieis of Al and Cu are: kal = 205 W/m K and kcu = 385 W/m K. The rate at which heat is conducted is:

a) 10W

b) 9W

c) 7.9W

d) 12W

E) 11W

2. Relevant equations

Q = (kA[tex]\Delta[/tex]T)t/L

3. The attempt at a solution

I couldn't figure out how to fit the t (time) into this at all, so perhaps i'm using the wrong equation?

k values were all given

A = 0.0004m2

[tex]\Delta[/tex]T = 170-30 = 140C

Otherwise, I am also confused with this one. Do I need to find a seperate Q for both materials (Al and Cu)? And if so, what happens to that t (time) value?

QUESTION FOUR:

1. The problem statement, all variables and given/known data

A proton is fixed in place. A second proton is released from rest at a point 1.0cm away What will be the velocity of the second proton when it is a very large distance from the first?

2. Relevant equations

Not sure, Wnc = 1/2 mvf^{2}???

3. The attempt at a solution

Proton at rest = vo = 0m/s

Proton mass = 1.67 x 10^{-27}kg

QUESTION FIVE:

1. The problem statement, all variables and given/known data

A bus is moving at 37.00m/s towards a wall. The sound from the bus has an original wavelength of 0.1500m. The sound from the bus reflects off the wall. What frequency sound doesan observer on the moving bushear from the reflection??

2. Relevant equations

Moving Observer: fo = fs (1 + vo/v)

v = [tex]\lambda[/tex]f

3. The attempt at a solution

Is this doppler effect??

I'm assuming the wavelength will double given that it reflects off a wall?

So, [tex]\lambda[/tex] = 2(0.1500m) = 0.300m

vo = 37.00m/s

Since v = [tex]\lambda[/tex]f

vi = [tex]\lambda[/tex]fi

f = v / [tex]\lambda[/tex]

= (343m/s)(0.1500) = 2286.667hz

Subbing into equation:

fo = (2286.667hz)(1 + 37m/s / 343m/s) = 2533hz

Is that correct??? I don't think it is because doing that didn't account for the reflection off the wall - unless I misunderstand how that works?

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Thanks for any help!!

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# Homework Help: *Various Questions: EPE Proton, Sound Intensity, Sound Frequency, Heat Conduction,

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