# 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