How Much Would You Weigh on a Smaller Planet?

[brad sue]

Hey!
I need help for this problem.

The mass of a hypothetical planet is 1/100 that the Earth and its radius is 1/4 that of the Earth. If a person weigths 150 lb on the earth, what would he weigth on his planet?

I tried the formula g=GM/r^2 by doing a ratio but I do not find the right answer.

Thank you
B

 

[lightgrav]

well, g = GM/r^2 , all right ...
show me your actual work and I'll find your error.

(I suspect that you forgot to square the ¼ ...)

 

[Pengwuino]

What exactly did you do? It's not going to be a linear relationship...

 

[brad sue]

well, g = GM/r^2 , all right ...
show me your actual work and I'll find your error.
(I suspect that you forgot to square the ¼ ...)

g_p= GM_p/R_p²
g_p= GM_e/R_e²
g_e/g_p=(M_e/M_p)*(R_p/R_e)=100/4=25

 

[Pengwuino]

Yup, you forgot to square the denominator. It's R^2 remember?

 

[lightgrav]

yeah ... you know what that "2" is for ?

If you're likely to forget the square (most people are), write the r^2 as r . r .

 

[brad sue]

Yup, you forgot to square the denominator. It's R^2 remember?

OOPS! thank you