When the speed of a moving object is doubled, what happens to its kinetic energy?

1 The work done on a body moving in a circular path is zero. Justify. 2 Calculate the kinetic energy of a body of mass 2kg moving with a velocity of 0.1 metre per second. 4 Which would have a greater effect on the kinetic energy of an object, doubling the mass or doubling the velocity? 5 If acceleration due to gravity is 10m/s², what will be the potential energy of a body of mass 1kg kept at a height of 5m?