physics mechanics

[yingao]

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if an animal were transported to a planet made up of the same material as earth, but with twice its radius, how would the animals weight be affected?

1. it would weigh one fourth as much as on earth
2. it would weigh twice as much as on earth

I calculated by using gravitational force equation and got one fourth as much as on earth, but that is not the answer!! 🙁

 

[Donald Juan]

The problem is that you are not taking into account that the new planet would have a mass 8 times that of earth [ (2 x radius of earth)^3 ] Note that the mass of the planet is proportional to the volume since both earth and the planet have the same densities, and mass = density x volume. So, the increased mass divided by the increased radius is 8/4 = 2.

 

[yingao]

ooh, i see, thx