Question

A force of 5.25 newtons acts on an object of unknown mass at a distance of 6.9..*.108 meters from the center of Earth. To increase the force to 2.5 times its original value, how far should the object be from the center of Earth?

Answer 1

1. force is due to gravity
$$F\propto{1\over r^2}\\
{F_1\over F_2}={r_2^2\over r_1^2}$$
you have F1, F2, and r1
find r2