Relationship between mass/gravity/speed

[aturocy]

Homework Statement

Assume that a planet just like Earth is orbiting the bright star vega at a distance of 1AU. The mass of vega is twice that of the sun.
a. How fast is the Earth like planet traveling around vega?
b. How long will it take to complete one orbit around vega?

Homework Equations

P2= r3 x (4x3.14/GM2)

The Attempt at a Solution

Is the relationship directly proportional? will the speed of the planet be 365.24days per period/2 ? or does the formula above need to be pluged into a separate formula to determin speed? Or is the escape velocity formula needed?

 

[I like Serena]

Perhaps you'd better use the formula for the equality of the gravitational force and the centripetal force?

 

[aturocy]

Thank you, I wound up thinking about it some more and I divided 1 Earth orbit period by the square root of 2 to get the days of rotation. Then I could calculate the speed of the orbit based on orbit perimeter divided by time. It seems to make sense, hopefully I worked it out with the right formula this time.