What is the new weight of a 10kg object on a planet that has twice the earths mass. (assume that the radius of the planet is the same as earths)

Weight = (mass) x (acceleration of gravity).

Acceleration of gravity on a planet's surface is proportional to

(planet's mass) / (planet's radius) ².

On Earth's surface, acceleration of gravity is 9.8 m/s².

Weight of 10 kg mass = (10 kg) x (9.8 m/s²) = 98 newtons.

On the surface of a planet with twice the Earth's mass

all stuffed into the same radius, the acceleration of gravity

would be 19.6 m/s² ... double what it is on Earth.

Weight of 10 kg would be (10 kg) x (19.6 m/s²) = 196 newtons ...

double its Earth weight.