# Unit Conversion (mass, radius )

## Homework Statement

In January 2006, astronomers reported the discovery of a planet comparable in size to the earth orbiting another star and having a mass of about 5.5 times the earth's mass. It is believed to consist of a mixture of rock and ice, similar to Neptune. Take mass earth 5.97 x 10 ^24 and radius earth 6.38x10^6.

If this planet has the same density as Neptune (1.76 g/cm^3), what is its radius expressed in kilometers?

What is its radius expressed as a multiple of earth's radius?

D=MV

## The Attempt at a Solution

My attempt:

I got (5.97x10^24kg earth's mass / 6380 km earth's radius) x (.00176 kg mass of unknown planet mass / x the radius of the unknown planet)

= 1.068676422 x 10^-21

The answer does not seems right, I did convert each unit accordingly.

Please and thank you in advance.

## Answers and Replies

hage567
Homework Helper
Well for one thing, density is M/V, not M*V. I don't understand what you are doing. Where's your use of the density equation?

Nevermind, I solved it using the formula for finding the volume of sphere. In which it lead me to the final radius of 1.65 x 10 ^4 km.

Thank you anyways. I just noticed the mistake of the D=M/V formula I stated before, :surprised can't believe I did that.