Homework Help: Need help with physics question

1. Sep 5, 2004

ramin86

I'm really bad at physics and need help with the following question:

Two spheres are cut from a certain uniform rock. One has radius 4.95 cm. The mass of the other is seven times greater. Find its radius.

2. Sep 5, 2004

jcsd

The average density of an object is:

$$\rho = \frac{m}{V}$$

Where m is mass and V is volume

The volume of a sphere is:

$$V = \frac{4\pi}{3} r^3$$

These are the only two formulas you need.

3. Sep 5, 2004

Tide

Does this look familiar?

$$\frac {R_1}{R_2} = \left(\frac{M_1}{M_2}\right)^{\frac{1}{3}$$

4. Sep 5, 2004

ramin86

Alright, well I got a volume of 508.05 for the sphere with a radius of 4.95, but still not exactly sure of where to go from here.

5. Sep 5, 2004

ramin86

Okay, nevermind, I got the answer at 9.469