Physics Problem

algebrapro18

TCS Member
Thread starter
Alpha Cat
Joined
Apr 16, 2008
Messages
498
Purraise
1
Location
Chicagoland
Given that The radius of the earth's orbit around the sun (assumed to be circular) is 1.50 \\times 10^{8}\\; {\
m km}, and the earth travels around this orbit in 365 days, what is the orbital velosity of the earth?

I tried to do the following

x = 1/2 vt
1.5x10^11 meters = (.5)(v)(31536000 seconds)
1.5x10^11 meters = 1.5768x10^7 seconds * v
9512.94 meters/second = velocity

but this isn't the right answer, what am I doing wrong?
 

going nova

TCS Member
Top Cat
Joined
Jan 31, 2008
Messages
1,951
Purraise
12
You have a radius but didnt convert it to the circumference of the circular orbit?
2*pi*1.5*10^8 meters?

Why did you use the equation x = 1/2*v*t? Where does the 1/2 come from? Distance = velocity * time.
 
  • Thread Starter Thread Starter
  • #3

algebrapro18

TCS Member
Thread starter
Alpha Cat
Joined
Apr 16, 2008
Messages
498
Purraise
1
Location
Chicagoland
it comes from the equation

x(final) - x(initial) = Time(v(initial)+v(final))/2

well all inital values can be considered 0 so this simplifies down to

x = 1/2vt
 

yosemite

TCS Member
Veteran
Joined
Apr 26, 2001
Messages
23,313
Purraise
81
Location
Ingersoll, ON
I'm sorry, but I just have to ask - do you think the folks here should be doing your homework for you?

And folks who are doing the homework - do you think that's fair?

If you need assistance you should be asking your prof.
 

februa

TCS Member
Super Cat
Joined
Dec 9, 2004
Messages
1,143
Purraise
1
Location
Toronto, Ontario
Orbital velocity as I know it is calculated by

v= sqrt (GM/r)

where G is gravitational constant (6.674 x 10^-11 m^3 kg^-1 s^-2)
and M is central mass of object (Earth) (5.9742 x 10^24 kg)

Try these numbers and see if it matches with your "right" answer.

Edit: Your method calculates linear velocity. With orbital, velocity increases inversely as the square root of the orbital radius... hence my earlier equation.
 

yosemite

TCS Member
Veteran
Joined
Apr 26, 2001
Messages
23,313
Purraise
81
Location
Ingersoll, ON
Well apparently they don't mind doing your homework then.
I hope they get some of the credit when you hand in your papers.
 

going nova

TCS Member
Top Cat
Joined
Jan 31, 2008
Messages
1,951
Purraise
12
Originally Posted by algebrapro18

it comes from the equation

x(final) - x(initial) = Time(v(initial)+v(final))/2

well all inital values can be considered 0 so this simplifies down to

x = 1/2vt
V initial is equal to V final... so this would give a 2v on the top. So 2 in the numerator and 2 in the denominator would cancel out... so your equation has a 1/2 that doesn't need to be there.

Re: Februa's equation- though useful, you don't really need it to solve the problem. You're making way too much work out of simple algebra. You only really need x = vt

Originally Posted by Yosemite

I'm sorry, but I just have to ask - do you think the folks here should be doing your homework for you?

And folks who are doing the homework - do you think that's fair?

If you need assistance you should be asking your prof.
I didn't actually do the work, but am trying to explain how he ought to do it. Although, to be honest, it's probably more important to know how to get an answer than to actually get one. I do agree that he should ask the professor, and it couldn't hurt to work on the homework with classmates...
 

mrblanche

TCS Member
Veteran
Joined
Jan 28, 2008
Messages
12,578
Purraise
119
Location
Texas
Gee, that's what I thought. Calculate the distance around the orbit, and divide it by the number of hours it takes in order to get a velocity. Unless I'm seriously overlooking something (not impossible), this is a pretty good first semester high school math problem (and no algebra needed).
 

februa

TCS Member
Super Cat
Joined
Dec 9, 2004
Messages
1,143
Purraise
1
Location
Toronto, Ontario
If its that simple a problem, isnt the answer just v=distance/time
where distance = 2pi(1.5 x 10^11 m)

and time is= 31536000 seconds (per year)

=29885.8 m/s
 

going nova

TCS Member
Top Cat
Joined
Jan 31, 2008
Messages
1,951
Purraise
12
Originally Posted by Februa

If its that simple a problem, isnt the answer just v=distance/time
where distance = 2pi(1.5 x 10^11 m)

and time is= 31536000 seconds (per year)

=29885.8 m/s
I was thinking that it was something like that since the only given he mentioned was the radius of the orbit. If so, I find it a little bit silly because it isn't much of a physics problem and should be in his realm of comfort.
 
Top