A body is moving on a frictionless horizontal surface under the influence of a constant force F→=3i^+4j^ m/sec2.  When the velocity of the body is 2i^−3j^ m its kinetic energy.

(3)when   v→=2i^−3j^ m/s, rate of work done on the body F→.v→=3i^+4j^. 2i^−3j^J/s=6−12  J/S=−6J/S.So by work - energy Theorem, kinetic energy is decreasing at a rate of 6 Joule / sec.