What happens to the kinetic energy of a body when: a) the mass of the body is doubled at constant velocity? b) the velocity of the body is doubled at constant mass? c) the mass of the body is doubled but the velocity is reduced to half?

the answer is b, have negligible mass

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.