a) Two lead balls with masses 5.20kg and 0.250kg are place with their centres 50.0cm apart. With what gravitational force do they attract each other?

b) At Earth's surface g=9.806m/s². Assuming the Earth to be a sphere of radius 6.371x10^6, find the mass of the Earth.

Take G = 6.67x10^-11Nm²kg^-2

a) Use: G(Mb1)(Mb2)/r^2

(6.67x10^-11)(5.20)(0.250)/(0.5)=3.5x10^-10 (2s.f.)

b) Use: g=GM/r^2

9.806x(6.371x10^6)^2/6.67x10^-11=6.0x10^24 (2s.f.)

Hopefully my calculations are good. Please check if ok someone?(Nerd)