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
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?