Weight on a Planet with Twice the Mass and Three Times the Radius

[tandoorichicken]

Help with this: I don't know how to not use the mass or radius of Earth.

Determine what your weight would be on a planet that had twice times the mass of the Earth and three times Earth's radius. (there is a was to figure this our without knowing the radius or the mass of the Earth.)

 

[Doc Al]

Use the universal law of gravity. You don't need to know the mass or radius of the earth. Compare the weight on Earth to the weight on the other planet. Think in terms of ratios.

 

[ShawnD]

now let's say the old weight is equal to 1, you'll see why.
Old weight:
= Gm1m2/r^2
= 1


New weight:
= G(2m1)m2/(3r)^2
= 2Gm1m2/9r^2
= (2/9)Gm1m2/r^2
= (2/9)(1)
= 2/9


your weight on this new planet will 2/9 times your current weight.