(a) The velocity of the object on the x-axis is 6 m/s, while on the y-axis is 2 m/s, so the magnitude of its velocity is the resultant of the velocities on the two axes:
And so, the kinetic energy of the object is
(b) The new velocity is 8.00 m/s on the x-axis and 4.00 m/s on the y-axis, so the magnitude of the new velocity is
And so the new kinetic energy is
So, the work done on the object is the variation of kinetic energy of the object:
And so, the kinetic energy of the object is
(b) The new velocity is 8.00 m/s on the x-axis and 4.00 m/s on the y-axis, so the magnitude of the new velocity is
And so the new kinetic energy is
So, the work done on the object is the variation of kinetic energy of the object: