Remark
I take it that you want to know the ratio of the radii. If this is not correct, leave a comment below my answer.
You could do this by giving the spheres a definite volume, like 1 and 8 and then solve for r for one of them and then use the other sphere to find it's radius. It is not exactly the best way, and if you are going to to a physics class you want to be doing this using cancellation.
Step One
Set up the Ratio for the volumes.
[tex] \frac{V_1}{V_2} = \frac{1}{8} [/tex]
Step Two
Setup the equation for V1/V2 using the definition for a sphere. V = 4/3 pi r^3
[tex] \dfrac{1}{8} = \frac{ \frac{4}{3} \pi( r_1)^3 }{ \frac{4}{3} \pi( r_2)^3 } [/tex]
Step Three
Cancel the 4/3 and pi on the top and bottom of the fractions on the right.
You are left with 1/8 = (r1)^3/ (r2)^3
Step Four
Take the cube root of both sides.
cube root 1/8 = 1/2
Cube root of (r1)^3 = r1
Cube root of (r2)^3 = r2
Step Five
Answer
[tex]\frac{r_1}{r_2} = \frac{1}{2} [/tex] Answer <<<<<<<
