posted by Suzy .
A hovercraft of mass 77.0 kg can move on a horizontal surface, the x-y plane. A single unbalanced force acts on the hovercraft, but the size of the force is unknown. The hovercraft initially has a velocity of 6.0 m/s in the positive x direction and some time later has a velocity of 9.0 m/s in the positive y direction. How much work is done on the hovercraft by the force during this time?
How long does the velocity change take? "Some time later" does not provide enough information.
You can get the force from the momentum change and the time interval.
On second thought, the work done equals the kinetic energy change. You can solve for that, no matter how long the velocity change takes. The direction changes don't matter in the result.