SOLUTION: hey i didnt know where else to go with this.... its asking me: <p> a person's weight on the surface of a planet is directly proportional to the mass of the planet and inversel

Question 98001: hey i didnt know where else to go with this....
its asking me:

a person's weight on the surface of a planet is directly proportional to the mass of the planet and inversely proportional to the square of the radius of the planet.
if a man weighs 180 pounds on earth, how much will he weigh on a planet that is 2 times as massive as earth and has 3 times the radius of earth?

im very confused by the directly and inversely proportional things and i've been trying to do this problem i just don't know where to get started...any help would be greatly appreciated : ) thanks

Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
directly means as one thing gets larger, another thing also gets larger .. x=ky (where k is a constant)

inversely means as one thing gets larger, another thing gets smaller ... xy=k

let w=weight, if m is the mass and r is the radius; then w(r^2)=km ... w=km/(r^2)

when r=1 and m=1, w=180; so k=180 ... w=180(1)/(1^2)

when r=3 and m=2 ... w=180(2)/(3^2) ... w=40

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