What is the weight of an object on Earth with a mass of 12 kg?

The object will always have 12 kg of mass - on Earth, in space, on the Moon, on Jupiter, everywhere. Mass is invariant. Weight depends on gravity. The Moon's gravity is approximately 1/6 of Earth's (not bothering to look up the exact ratio), so the object would weigh about 2 kg.

A) circumference = 2 pi r = 2pi(6)= 37.7 cm = 0.377 m

b) speed = 4 x circumference = 0.377 x  4 = 1.51 m/s
 
c) angular speed is proportional to distance from the center. if radious is halved, the speed is halved. therefore speed at 3 cm = 1.51 /2 = 0.75 m/s