1. The problem statement, all variables and given/known data A 3.00kg object has velocity 7.00j m/s. Then, a total force 12.0i N acts on the object for 5.00s. Find the final kinetic energy from 1/2mvf^2 = 1/2mvf . vf 2. Relevant equations 3. The attempt at a solution i got 1/2 * 3 * (20i+7j)(20i+7j) then 600j^2 + 210ij + 73.5j^2 but the answer is 673.5 J, why? since j.j =i.i=1 and i.j=0?