The gravitational field strength of an unknown planet is 15.5 N/kg on its surface. Calculate the value of “g” if the planets mass and radius were both doubled. Hint: Use variation

Question

The gravitational field strength of  an unknown planet is 15.5 N/kg on its surface. Calculate the value of “g” if the planets mass and radius were both doubled. Hint: Use variation

anonymous · Answer

you dont have any more information like the radius?

anonymous · Answer

No. You don't need it. You need to solve it using variation.

superdavesuper · Answer

Use F=mg to calculate the original g value first....

anonymous · Answer

f= m/r^2 G not mg

superdavesuper · Answer

well 15.5N=1kg*g so original g=15.5m/s^2

superdavesuper · Answer

then yes use @SalvadorV 's eqn of f=Gm/r^2 to calculate the new g

anonymous · Answer

I know the final answer is 7.25N/kg but I can't get to it using variation.

superdavesuper · Answer

new m = 2x original m
new r = 2x original r

so what will the new g be if g depends on m/r^2?

anonymous · Answer

new g will be half of original g?

superdavesuper · Answer

yes :)