Standards of Length, Mass, and Time

[knightassassin]

Two spheres are cut from a certain uniform rock. One has radius 4.30 cm. The mass of the other is two times greater. Find its radius.


Not sure what equations to use for it

I am not sure how to attempt this problem?

 

[Dick]

Mass is volume times density. 'Uniform' rock means you can assume the two rocks have the same uniform density. Now do you know a relation between the radius of a sphere and the volume?

 

[knightassassin]

Volume equals (4/3)pi radius^3

 

[Dick]

Good then you are all set to go. Try solving it.

 

[knightassassin]

Thanks I got it. So I set the two relations equal to each other m1/v1=m2/v2. Substitute volume for their equation of (4/3)pi radius^3 and solve for r2.

 

[knightassassin]

The answer I got was 5.4 cm, which is right thanks again.