# Calculate the time required in millions of years for one orbit.

1. Aug 3, 2010

### quah13579

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

The solar system is situated 26,000 light years from the centre of our galaxy, the Milky Way, and it orbits the centre at a speed of 220 km/sec.

Calculate the time required in millions of years for one orbit.
(NOTE: The circumference of a circle = 2 pi r where r is its radius.)

2. Relevant equations
3. The attempt at a solution

2. Aug 3, 2010

### tiny-tim

welcome to pf!

hi quah13579! welcome to pf!

(have a pi: π )

find how to convert light years into km, and then calculate the length of the circumference of the orbit …

what do you get?

3. Aug 3, 2010

### quah13579

Re: welcome to pf!

9,460,730,472,580.8(light-year in km) * 26000(of light-years around) * 2 * 3.1415926535 = 1545531590213152572.8104183193436(km) / 220(km/sec) / 60(sec/min) / 60 (min/hrs) / 24 (hrs/days) / 365.25(days/years) = 222613367.04559 years
is it right?

4. Aug 3, 2010

### tiny-tim

hmmm … never never never use all those figures (you'll lose marks in the exam if you do) … 3 sig figs should usually be more than enough