Help again please!

[Jared]

Hey guys! Only one more physics test to go before I'm done with physics, but I haven't a clue on how to solve any of these problems yet...

If anyone could give me a clue I would appreciate any information that you guys could provide...;-)





I have some ideas on this one but not sure if they are right...:-)

[gw]

Jared,

Your second problem is one in Special Relativity.  You should start by looking in your text at the definition of simultaneity.  If two events happen at the same time, as the marshal thinks is the case, it just means that light from the two events reached him at the same time.  Knowing the relative positions of everyone and the speed of the marshal you have to figure out the distance that the light from each shooter traveled to reach the train and then decide who fired first based on how long the light took to reach the marshal from each.

It would also be helpful to draw some space-time diagrams for each of the three observers so you can see what's going on from each's point of view.

And, finally, the Lorentz equations will tell you exactly how much time dilates for each observer here.

gw

[gw]

Jared,

And some thoughts on question 4.  I'm sure your text book tells you how relativistic mass is related to velocity and you know how to relate mass to kinetic energy.  So it seems to me that the same problem in a different light would be to find the speed of a particle when its relativistic mass is twice its rest mass.  

gw

[Jared]

Thanks for the information GW, I appreciate the time and effort that you put into it for me...;-)

Will look into all of this tonight after school/work and see if I can get somewhere...:-)

[flyboy 28]

This is freaky. Jared is in college, and I am in 8th grade, and we're learning the same thing?!?!?!

Although I still have no idea how to do it.

[Jared]

allrighty fellas quick update...

figured out problems three and four... the following is what three and four will look like when solved...

Question #3
An observer looks at a source through a grating having 1000 slits per cm. If the wavelength is 550nm, how many images of the source can be seen? (Hint: For what order would theta be + or - 90 degrees)

Answer:
d = grating spacing
deviation angle = 30 degs
λ = wave length of light
n = spectral order
N = no of lines / cm = 1000
N= 1/d or d = 1/N = 1/103 cm = 10-3 cm = 10 -5 m
nλ = d Sin 
λ = 550 nm = 550 x 10 -9 m.
Maximum number of images will be seen for greatest angle of deviation i.e.  = + or - 90 degs
hence Sin  = + or - 1
therefore the order numbers for the visible spectrum for the grating are limited to
n < = d / λ = 10 -5 / 550 x 10 -9 = 18.2
hence 18 complete orders will be observed, or 36 images;18 on each side of central maximum
(x-1)mo c2 = mo c2
{1 / (1 - v2 / c2) - 0.5} - 1 = 1
1 / (1 - v2 / c2) - 0.5 = 2
1 - v2 / c2 = 1/4
v = 0.866c


Question #4
What is the speed of a particle
A.  whose kinetic energy is equal to twice its rest energy and
B.  whose total energy is equal to twice its rest energy?

Answer:
I used the following:

E = mc

[Jared]

Still looking for answers on one and two...;-)

[Jared]

all right figured out number one, and number two doesn't look so bad using the book, will post answers when I figure the second one out....:-)

[Jared]

Allrighty! The farthest fighter shot 167 nano seconds before the closer one...

this is the time that it took the light to travel from the farther fighter to the closer fighter, who then shot his gun!

and to the marshal they both shot at the same time! :-)

[Jared]

By the way, got my labs back from the class the other day, and I got a total of 97.6% for the full semester...

Yay! 5 credit hours of A! That'll bring the GPA UP!

[Stormtropper]

LOL Jared, I think that you invented a new way to cheat on homework.

BTW, I'm older than flyboy_28, I'm a Freshman (which sucks because we are the objects of laughter to the seniors).

[Jared]

lol, Freshmen huh? I never had a problem with that at my school..

I was the most popular guy in class, captain of the football team, prom king...

why even class president....:-)

Oh, by the way, did I mention that I was homeschooled?  ;D

Now in the fall I will become a senior in college! :-) Yay! Another year and I can finally get a real job! :-)

[Jared]

by the way, our prof. tells us with each test that we can use any knowledge that we can from any source in order to get the right answers...;-)

[Stormtropper]

Too bad there wasn't a prom queen at your school.

[Jared]

lol... If I had been in West virginia, or Jersey, I suppose the prom queen could have been my sister...

BUT, since the hay wagon doesn't swing that way, no how!, I was stuck by meself....